Present kernel detection progress in kernel picker/status (#166294)

* Experimental kernel detection task

* Update kernel detection progress

* no need for start/end now.

* Enforce proposed api

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

@@ -4,4 +4,17 @@
  *--------------------------------------------------------------------------------------------*/
 
 declare module 'vscode' {
+	export interface NotebookControllerDetectionTask {
+		/**
+		 * Dispose and remove the detection task.
+		 */
+		dispose(): void;
+	}
+
+	export namespace notebooks {
+		/**
+		 * Create notebook controller detection task
+		 */
+		export function createNotebookControllerDetectionTask(notebookType: string): NotebookControllerDetectionTask;
+	}
 }