Support kernel source actions update. (#171781)

src/vscode-dts/vscode.proposed.notebookKernelSource.d.ts

@@ -22,6 +22,10 @@ declare module 'vscode' {
 	}
 
 	export interface NotebookKernelSourceActionProvider {
+		/**
+		 * An optional event to signal that the kernel source actions have changed.
+		 */
+		onDidChangeNotebookKernelSourceActions?: Event<void>;
 		/**
 		 * Provide kernel source actions
 		 */