Add CustomDocumentContentChangeEvent

For #77131

- Rename `onDidEdit` to `onDidChange`
- Allow custom editors to fire a `CustomDocumentContentChangeEvent` that only marks the editor as dirty but does not enable undo/redo. The only way for editor to get out of this dirty state is to either save or revert the file

src/vs/workbench/api/common/extHost.protocol.ts

@@ -615,6 +615,7 @@ export interface MainThreadWebviewsShape extends IDisposable {
 	$unregisterEditorProvider(viewType: string): void;
 
 	$onDidEdit(resource: UriComponents, viewType: string, editId: number, label: string | undefined): void;
+	$onContentChange(resource: UriComponents, viewType: string): void;
 }
 
 export interface WebviewPanelViewStateData {