docs(service-worker): add example app for SwPush API docs (#32139)

Previously, the `SwPush` API docs were using hard-coded code snippets.

This commit switches to using code snippets from an actual example app,
which ensures that the code shown in the docs will at least continue to
compile successfully.

PR Close #32139

packages/examples/service-worker/push/module.ts

@@ -0,0 +1,66 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+// tslint:disable: no-duplicate-imports
+import {Component, NgModule} from '@angular/core';
+import {BrowserModule} from '@angular/platform-browser';
+import {ServiceWorkerModule} from '@angular/service-worker';
+// #docregion inject-sw-push
+import {SwPush} from '@angular/service-worker';
+// #enddocregion inject-sw-push
+// tslint:enable: no-duplicate-imports
+
+const PUBLIC_VAPID_KEY_OF_SERVER = '...';
+
+@Component({
+  selector: 'example-app',
+  template: 'SW enabled: {{ swPush.isEnabled }}',
+})
+// #docregion inject-sw-push
+export class AppComponent {
+  constructor(readonly swPush: SwPush) {}
+  // #enddocregion inject-sw-push
+
+  // #docregion subscribe-to-push
+  private async subscribeToPush() {
+    try {
+      const sub = await this.swPush.requestSubscription({
+        serverPublicKey: PUBLIC_VAPID_KEY_OF_SERVER,
+      });
+      // TODO: Send to server.
+    } catch (err) {
+      console.error('Could not subscribe due to:', err);
+    }
+  }
+  // #enddocregion subscribe-to-push
+
+  private subscribeToNotificationClicks() {
+    // #docregion subscribe-to-notification-clicks
+    this.swPush.notificationClicks.subscribe(
+        ({action, notification}) => {
+            // TODO: Do something in response to notification click.
+        });
+    // #enddocregion subscribe-to-notification-clicks
+  }
+  // #docregion inject-sw-push
+}
+// #enddocregion inject-sw-push
+
+@NgModule({
+  bootstrap: [
+    AppComponent,
+  ],
+  declarations: [
+    AppComponent,
+  ],
+  imports: [
+    BrowserModule,
+    ServiceWorkerModule.register('ngsw-worker.js'),
+  ],
+})
+export class AppModule {
+}