testing: fix loading indicators, add progress during initial test discovery

src/vs/workbench/api/browser/mainThreadTesting.ts

@@ -46,6 +46,13 @@ export class MainThreadTesting extends Disposable implements MainThreadTestingSh
 		this.testService.unregisterTestController(id);
 	}
 
+	/**
+	 * @inheritdoc
+	 */
+	$updateDiscoveringCount(resource: ExtHostTestingResource, uriComponents: UriComponents, delta: number): void {
+		this.testService.updateDiscoveringCount(resource, URI.revive(uriComponents), delta);
+	}
+
 	/**
 	 * @inheritdoc
 	 */