Do not throw on empty registered headless task (#24671)

Summary:
Start a `HeadlessJsTaskService` on Android without registered is dangerous on apps because `HeadlessJsTaskService` will acquire a [`PARTIAL_WAKE_LOCK`](https://developer.android.com/topic/performance/vitals/wakelock), without calling `onHeadlessJsTaskFinish` this lock won't release until timeout(if exist). This lock will prevent the android device from sleeping.

Although on JS will throw an error if no headless tasks registered, but it's hard to notice while app in the background. No visual information is displayed.

This PR will log a warning instead of Error, and just mark the task to finished on native if nothing registered in order to release the wake lock.

[Android] [Fixed] - Fix unexpected PARTIAL_WAKE_LOCK when no headless tasks registered.
Pull Request resolved: #24671

Differential Revision: D15164310

Pulled By: cpojer

fbshipit-source-id: 05b62017ba094d0faabc2848dc8bb6c26101321b

Author: timwangdev

Libraries/ReactNative/AppRegistry.js

@@ -260,7 +260,9 @@ const AppRegistry = {
   startHeadlessTask(taskId: number, taskKey: string, data: any): void {
     const taskProvider = taskProviders.get(taskKey);
     if (!taskProvider) {
-      throw new Error(`No task registered for key ${taskKey}`);
+      console.warn(`No task registered for key ${taskKey}`);
+      NativeModules.HeadlessJsTaskSupport.notifyTaskFinished(taskId);
+      return;
     }
     taskProvider()(data)
       .then(() =>