Improve Undo/Redo menu items

* Make Undo/Redo menu items disabled when clicking it does nothing.
    * Context menu of `TextEdit`
    * Context menu of `LineEdit`
    * Editor's Scene menu
    * Script editor's Edit menu and context menu (for Script and Text)
* Make editor undo/redo log messages translatable.
* Mark `UndoRedo`'s `has_{un,re}do()` methods as `const`.
* Expose `TextEdit`'s `has_{un,re}do()` to scripts since `{un,re}do()` are already available.

2 files changed, 4 insertions, 4 deletions

diff --git a/core/object/undo_redo.cpp b/core/object/undo_redo.cpp
index adf068eb2f..b7d2bac96d 100644
--- a/core/object/undo_redo.cpp
+++ b/core/object/undo_redo.cpp
@@ -405,11 +405,11 @@ String UndoRedo::get_current_action_name() const {
 	return actions[current_action].name;
 }
 
-bool UndoRedo::has_undo() {
+bool UndoRedo::has_undo() const {
 	return current_action >= 0;
 }
 
-bool UndoRedo::has_redo() {
+bool UndoRedo::has_redo() const {
 	return (current_action + 1) < actions.size();
 }
 
diff --git a/core/object/undo_redo.h b/core/object/undo_redo.h
index 8f009830e3..d1ce252d86 100644
--- a/core/object/undo_redo.h
+++ b/core/object/undo_redo.h
@@ -121,8 +121,8 @@ public:
 	String get_action_name(int p_id);
 	void clear_history(bool p_increase_version = true);
 
-	bool has_undo();
-	bool has_redo();
+	bool has_undo() const;
+	bool has_redo() const;
 
 	uint64_t get_version() const;