feat(service-worker): Add typing for messagesClicked in SwPush service (#25860)

- Properly type messagesClicked Observable stream
- Add new NotificationObject interface

PR Close #25860

packages/service-worker/src/low_level.ts

@@ -52,6 +52,10 @@ interface StatusEvent {
   error?: string;
 }
 
+export interface NotificationObject extends NotificationOptions {
+  title: string; 
+}
+
 
 function errorObservable(message: string): Observable<any> {
   return defer(() => throwError(new Error(message)));

packages/service-worker/src/push.ts

@@ -10,7 +10,7 @@ import {Injectable} from '@angular/core';
 import {NEVER, Observable, Subject, merge} from 'rxjs';
 import {map, switchMap, take} from 'rxjs/operators';
 
-import {ERR_SW_NOT_SUPPORTED, NgswCommChannel, PushEvent} from './low_level';
+import {ERR_SW_NOT_SUPPORTED, NgswCommChannel, NotificationObject, PushEvent} from './low_level';
 
 
 /**
@@ -25,7 +25,21 @@ export class SwPush {
    */
   readonly messages: Observable<object>;
 
-  readonly messagesClicked: Observable<object>;
+  /**
+   * Emits the payloads of the received push notification messages as well as the action the user
+   * interacted with.
+   * If no action was used the action property will be an empty string `''`.
+   *
+   * Note that the `notification` property is __not__ a
+   * [Notification](https://developer.mozilla.org/en-US/docs/Web/API/Notification) but rather a
+   * [NotificationOptions](https://notifications.spec.whatwg.org/#dictdef-notificationoptions)
+   * object that also includes the notification `title`.
+   */
+  readonly messagesClicked: Observable < {
+    action: string;
+    notification: NotificationObject
+  }
+  > ;
 
   /**
    * Emits the currently active