Add a V-Sync editor setting

The editor setting makes it possible to tweak V-Sync status
independently of the project setting.

Use cases:

- Decrease input lag and increase editor responsiveness when editing
  a project that has V-Sync enabled.
- Avoid tearing when editing a project that has V-Sync disabled.

doc/classes/EditorSettings.xml

@@ -629,6 +629,11 @@
 			If [code]true[/code], editor main menu is using embedded [MenuBar] instead of system global menu.
 			Specific to the macOS platform.
 		</member>
+		<member name="interface/editor/vsync_mode" type="int" setter="" getter="">
+			Sets the V-Sync mode for the editor. Does not affect the project when run from the editor (this is controlled by [member ProjectSettings.display/window/vsync/vsync_mode]).
+			Depending on the platform and used renderer, the engine will fall back to [b]Enabled[/b] if the desired mode is not supported.
+			[b]Note:[/b] V-Sync modes other than [b]Enabled[/b] are only supported in the Forward+ and Mobile rendering methods, not Compatibility.
+		</member>
 		<member name="interface/inspector/float_drag_speed" type="float" setter="" getter="">
 			Base speed for increasing/decreasing float values by dragging them in the inspector.
 		</member>

doc/classes/ProjectSettings.xml

@@ -875,7 +875,7 @@
 			If [code]true[/code] subwindows are embedded in the main window.
 		</member>
 		<member name="display/window/vsync/vsync_mode" type="int" setter="" getter="" default="1">
-			Sets the V-Sync mode for the main game window.
+			Sets the V-Sync mode for the main game window. The editor's own V-Sync mode can be set using [member EditorSettings.interface/editor/vsync_mode].
 			See [enum DisplayServer.VSyncMode] for possible values and how they affect the behavior of your application.
 			Depending on the platform and used renderer, the engine will fall back to [b]Enabled[/b] if the desired mode is not supported.
 			[b]Note:[/b] V-Sync modes other than [b]Enabled[/b] are only supported in the Forward+ and Mobile rendering methods, not Compatibility.

editor/editor_node.cpp

@@ -345,6 +345,11 @@ void EditorNode::shortcut_input(const Ref<InputEvent> &p_event) {
 	}
 }
 
+void EditorNode::_update_vsync_mode() {
+	const DisplayServer::VSyncMode window_vsync_mode = DisplayServer::VSyncMode(int(EDITOR_GET("interface/editor/vsync_mode")));
+	DisplayServer::get_singleton()->window_set_vsync_mode(window_vsync_mode);
+}
+
 void EditorNode::_update_from_settings() {
 	_update_title();
 
@@ -758,6 +763,7 @@ void EditorNode::_notification(int p_what) {
 		} break;
 
 		case EditorSettings::NOTIFICATION_EDITOR_SETTINGS_CHANGED: {
+			_update_vsync_mode();
 			FileDialog::set_default_show_hidden_files(EDITOR_GET("filesystem/file_dialog/show_hidden_files"));
 			EditorFileDialog::set_default_show_hidden_files(EDITOR_GET("filesystem/file_dialog/show_hidden_files"));
 			EditorFileDialog::set_default_display_mode((EditorFileDialog::DisplayMode)EDITOR_GET("filesystem/file_dialog/display_mode").operator int());
@@ -6268,6 +6274,8 @@ EditorNode::EditorNode() {
 
 	FileAccess::set_backup_save(EDITOR_GET("filesystem/on_save/safe_save_on_backup_then_rename"));
 
+	_update_vsync_mode();
+
 	// Warm up the surface upgrade tool as early as possible.
 	surface_upgrade_tool = memnew(SurfaceUpgradeTool);
 	run_surface_upgrade_tool = EditorSettings::get_singleton()->get_project_metadata("surface_upgrade_tool", "run_on_restart", false);

editor/editor_node.h

@@ -584,6 +584,7 @@ private:
 	void _dropped_files(const Vector<String> &p_files);
 	void _add_dropped_files_recursive(const Vector<String> &p_files, String to_path);
 
+	void _update_vsync_mode();
 	void _update_from_settings();
 	void _gdextensions_reloaded();
 

editor/editor_settings.cpp

@@ -439,6 +439,9 @@ void EditorSettings::_load_defaults(Ref<ConfigFile> p_extra_config) {
 	// low FPS limits, the editor can take a small while to become usable after
 	// being focused again, so this should be used at the user's discretion.
 	EDITOR_SETTING_USAGE(Variant::FLOAT, PROPERTY_HINT_RANGE, "interface/editor/unfocused_low_processor_mode_sleep_usec", 100000, "1,1000000,1", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED)
+
+	EDITOR_SETTING(Variant::INT, PROPERTY_HINT_ENUM, "interface/editor/vsync_mode", 1, "Disabled,Enabled,Adaptive,Mailbox")
+
 	_initial_set("interface/editor/separate_distraction_mode", false);
 	_initial_set("interface/editor/automatically_open_screenshots", true);
 	EDITOR_SETTING_USAGE(Variant::BOOL, PROPERTY_HINT_NONE, "interface/editor/single_window_mode", false, "", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED)