C#: Add source generator for properties and exports default values

The editor no longer needs to create temporary instances to get the
default values. The initializer values of the exported properties are
still evaluated at runtime. For example, in the following example,
`GetInitialValue()` will be called when first looks for default values:

```
[Export] int MyValue = GetInitialValue();
```

Exporting fields with a non-supported type now results in a compiler
error rather than a runtime error when the script is used.

1 files changed, 13 insertions, 10 deletions

diff --git a/modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs b/modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs
index 4e27f4ed14..fe83e6a281 100644
--- a/modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs
+++ b/modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs
@@ -513,20 +513,23 @@ namespace GodotTools
 
         protected override void Dispose(bool disposing)
         {
-            base.Dispose(disposing);
-
-            if (_exportPluginWeak != null)
+            if (disposing)
             {
-                // We need to dispose our export plugin before the editor destroys EditorSettings.
-                // Otherwise, if the GC disposes it at a later time, EditorExportPlatformAndroid
-                // will be freed after EditorSettings already was, and its device polling thread
-                // will try to access the EditorSettings singleton, resulting in null dereferencing.
-                (_exportPluginWeak.GetRef() as ExportPlugin)?.Dispose();
+                if (IsInstanceValid(_exportPluginWeak))
+                {
+                    // We need to dispose our export plugin before the editor destroys EditorSettings.
+                    // Otherwise, if the GC disposes it at a later time, EditorExportPlatformAndroid
+                    // will be freed after EditorSettings already was, and its device polling thread
+                    // will try to access the EditorSettings singleton, resulting in null dereferencing.
+                    (_exportPluginWeak.GetRef() as ExportPlugin)?.Dispose();
 
-                _exportPluginWeak.Dispose();
+                    _exportPluginWeak.Dispose();
+                }
+
+                GodotIdeManager?.Dispose();
             }
 
-            GodotIdeManager?.Dispose();
+            base.Dispose(disposing);
         }
 
         public void OnBeforeSerialize()