[Editor] Better expose EditorDebuggerPlugin.

Now splitted into two classes:
- EditorDebuggerPlugin (RefCounted).
- EditorDebuggerSession (abstract).

This allows the EditorPlugin to be in control of the debugger plugin
lifecycle, be notified when sessions are created, and customize each of
them independently.

We should slowly transition the various profilers and captures in
ScriptEditorDebugger to their own plugins, and decouple
ScriptEditorDebugger from it's UI part (making it the "real"
EditorDebuggerSession potentially dropping the wrappers).

3 files changed, 146 insertions, 60 deletions

diff --git a/doc/classes/EditorDebuggerPlugin.xml b/doc/classes/EditorDebuggerPlugin.xml
index c3e0a995c6..10da1edd56 100644
--- a/doc/classes/EditorDebuggerPlugin.xml
+++ b/doc/classes/EditorDebuggerPlugin.xml
@@ -1,88 +1,88 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<class name="EditorDebuggerPlugin" inherits="Control" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+<class name="EditorDebuggerPlugin" inherits="RefCounted" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
 	<brief_description>
 		A base class to implement debugger plugins.
 	</brief_description>
 	<description>
 		[EditorDebuggerPlugin] provides functions related to the editor side of the debugger.
-		You don't need to instantiate this class; that is automatically handled by the debugger. [Control] nodes can be added as child nodes to provide a GUI for the plugin.
-		Do not free or reparent this node, otherwise it becomes unusable.
-		To use [EditorDebuggerPlugin], register it using the [method EditorPlugin.add_debugger_plugin] method first.
+		To interact with the debugger, an instance of this class must be added to the editor via [method EditorPlugin.add_debugger_plugin].
+		Once added, the [method _setup_session] callback will be called for every [EditorDebuggerSession] available to the plugin, and when new ones are created (the sessions may be inactive during this stage).
+		You can retrieve the available [EditorDebuggerSession]s via [method get_sessions] or get a specific one via [method get_session].
+		[codeblocks]
+		[gdscript]
+		@tool
+		extends EditorPlugin
+
+		class ExampleEditorDebugger extends EditorDebuggerPlugin:
+
+		    func _has_capture(prefix):
+		        # Return true if you wish to handle message with this prefix.
+		        return prefix == "my_plugin"
+
+		    func _capture(message, data, session_id):
+		        if message == "my_plugin:ping":
+		            get_session(session_id).send_message("my_plugin:echo", data)
+
+		    func _setup_session(session_id):
+		        # Add a new tab in the debugger session UI containing a label.
+		        var label = Label.new()
+		        label.name = "Example plugin"
+		        label.text = "Example plugin"
+		        var session = get_session(session_id)
+		        # Listens to the session started and stopped signals.
+		        session.started.connect(func (): print("Session started"))
+		        session.stopped.connect(func (): print("Session stopped"))
+		        session.add_session_tab(label)
+
+		var debugger = ExampleEditorDebugger.new()
+
+		func _enter_tree():
+		    add_debugger_plugin(debugger)
+
+		func _exit_tree():
+		    remove_debugger_plugin(debugger)
+		[/gdscript]
+		[/codeblocks]
 	</description>
 	<tutorials>
 	</tutorials>
 	<methods>
-		<method name="has_capture">
-			<return type="bool" />
-			<param index="0" name="name" type="StringName" />
-			<description>
-				Returns [code]true[/code] if a message capture with given name is present otherwise [code]false[/code].
-			</description>
-		</method>
-		<method name="is_breaked">
-			<return type="bool" />
-			<description>
-				Returns [code]true[/code] if the game is in break state otherwise [code]false[/code].
-			</description>
-		</method>
-		<method name="is_debuggable">
+		<method name="_capture" qualifiers="virtual">
 			<return type="bool" />
+			<param index="0" name="message" type="String" />
+			<param index="1" name="data" type="Array" />
+			<param index="2" name="session_id" type="int" />
 			<description>
-				Returns [code]true[/code] if the game can be debugged otherwise [code]false[/code].
+				Override this method to process incoming messages. The [param session_id] is the ID of the [EditorDebuggerSession] that received the message (which you can retrieve via [method get_session]).
 			</description>
 		</method>
-		<method name="is_session_active">
+		<method name="_has_capture" qualifiers="virtual const">
 			<return type="bool" />
+			<param index="0" name="capture" type="String" />
 			<description>
-				Returns [code]true[/code] if there is an instance of the game running with the attached debugger otherwise [code]false[/code].
+				Override this method to enable receiving messages from the debugger. If [param capture] is "my_message" then messages starting with "my_message:" will be passes to the [method _capture] method.
 			</description>
 		</method>
-		<method name="register_message_capture">
+		<method name="_setup_session" qualifiers="virtual">
 			<return type="void" />
-			<param index="0" name="name" type="StringName" />
-			<param index="1" name="callable" type="Callable" />
+			<param index="0" name="session_id" type="int" />
 			<description>
-				Registers a message capture with given [param name]. If [param name] is "my_message" then messages starting with "my_message:" will be called with the given callable.
-				Callable must accept a message string and a data array as argument. If the message and data are valid then callable must return [code]true[/code] otherwise [code]false[/code].
+				Override this method to be notified whenever a new [EditorDebuggerSession] is created (the session may be inactive during this stage).
 			</description>
 		</method>
-		<method name="send_message">
-			<return type="void" />
-			<param index="0" name="message" type="String" />
-			<param index="1" name="data" type="Array" />
+		<method name="get_session">
+			<return type="EditorDebuggerSession" />
+			<param index="0" name="id" type="int" />
 			<description>
-				Sends a message with given [param message] and [param data] array.
+				Returns the [EditorDebuggerSession] with the given [param id].
 			</description>
 		</method>
-		<method name="unregister_message_capture">
-			<return type="void" />
-			<param index="0" name="name" type="StringName" />
+		<method name="get_sessions">
+			<return type="Array" />
 			<description>
-				Unregisters the message capture with given name.
+				Returns an array of [EditorDebuggerSession] currently available to this debugger plugin.
+				Note: Not sessions in the array may be inactive, check their state via [method EditorDebuggerSession.is_active]
 			</description>
 		</method>
 	</methods>
-	<signals>
-		<signal name="breaked">
-			<param index="0" name="can_debug" type="bool" />
-			<description>
-				Emitted when the game enters a break state.
-			</description>
-		</signal>
-		<signal name="continued">
-			<description>
-				Emitted when the game exists a break state.
-			</description>
-		</signal>
-		<signal name="started">
-			<description>
-				Emitted when the debugging starts.
-			</description>
-		</signal>
-		<signal name="stopped">
-			<description>
-				Emitted when the debugging stops.
-			</description>
-		</signal>
-	</signals>
 </class>
diff --git a/doc/classes/EditorDebuggerSession.xml b/doc/classes/EditorDebuggerSession.xml
new file mode 100644
index 0000000000..faf528c143
--- /dev/null
+++ b/doc/classes/EditorDebuggerSession.xml
@@ -0,0 +1,86 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="EditorDebuggerSession" inherits="RefCounted" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		A class to interact with the editor debugger.
+	</brief_description>
+	<description>
+		This class cannot be directly instantiated and must be retrieved via a [EditorDebuggerPlugin].
+		You can add tabs to the session UI via [method add_session_tab], send messages via [method send_message], and toggle [EngineProfiler]s via [method toggle_profiler].
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="add_session_tab">
+			<return type="void" />
+			<param index="0" name="control" type="Control" />
+			<description>
+				Adds the given [param control] to the debug session UI in the debugger bottom panel.
+			</description>
+		</method>
+		<method name="is_active">
+			<return type="bool" />
+			<description>
+				Returns [code]true[/code] if the debug session is currently attached to a remote instance.
+			</description>
+		</method>
+		<method name="is_breaked">
+			<return type="bool" />
+			<description>
+				Returns [code]true[/code] if the attached remote instance is currently in the debug loop.
+			</description>
+		</method>
+		<method name="is_debuggable">
+			<return type="bool" />
+			<description>
+				Returns [code]true[/code] if the attached remote instance can be debugged.
+			</description>
+		</method>
+		<method name="remove_session_tab">
+			<return type="void" />
+			<param index="0" name="control" type="Control" />
+			<description>
+				Removes the given [param control] from the debug session UI in the debugger bottom panel.
+			</description>
+		</method>
+		<method name="send_message">
+			<return type="void" />
+			<param index="0" name="message" type="String" />
+			<param index="1" name="data" type="Array" default="[]" />
+			<description>
+				Sends the given [param message] to the attached remote instance, optionally passing additionally [param data]. See [EngineDebugger] for how to retrieve those messages.
+			</description>
+		</method>
+		<method name="toggle_profiler">
+			<return type="void" />
+			<param index="0" name="profiler" type="String" />
+			<param index="1" name="enable" type="bool" />
+			<param index="2" name="data" type="Array" default="[]" />
+			<description>
+				Toggle the given [param profiler] on the attached remote instance, optionally passing additionally [param data]. See [EngineProfiler] for more details.
+			</description>
+		</method>
+	</methods>
+	<signals>
+		<signal name="breaked">
+			<param index="0" name="can_debug" type="bool" />
+			<description>
+				Emitted when the attached remote instance enters a break state. If [param can_debug] is [code]true[/code], the remote instance will enter the debug loop.
+			</description>
+		</signal>
+		<signal name="continued">
+			<description>
+				Emitted when the attached remote instance exits a break state.
+			</description>
+		</signal>
+		<signal name="started">
+			<description>
+				Emitted when a remote instance is attached to this session (i.e. the session becomes active).
+			</description>
+		</signal>
+		<signal name="stopped">
+			<description>
+				Emitted when a remote instance is detached from this session (i.e. the session becomes inactive).
+			</description>
+		</signal>
+	</signals>
+</class>
diff --git a/doc/classes/EditorPlugin.xml b/doc/classes/EditorPlugin.xml
index 2289a373bf..806588d100 100644
--- a/doc/classes/EditorPlugin.xml
+++ b/doc/classes/EditorPlugin.xml
@@ -415,7 +415,7 @@
 		</method>
 		<method name="add_debugger_plugin">
 			<return type="void" />
-			<param index="0" name="script" type="Script" />
+			<param index="0" name="script" type="EditorDebuggerPlugin" />
 			<description>
 				Adds a [Script] as debugger plugin to the Debugger. The script must extend [EditorDebuggerPlugin].
 			</description>
@@ -599,7 +599,7 @@
 		</method>
 		<method name="remove_debugger_plugin">
 			<return type="void" />
-			<param index="0" name="script" type="Script" />
+			<param index="0" name="script" type="EditorDebuggerPlugin" />
 			<description>
 				Removes the debugger plugin with given script from the Debugger.
 			</description>