TF-1246: Enable FCM for Web browser

web/firebase-messaging-sw.js

@@ -0,0 +1,13 @@
+importScripts("https://www.gstatic.com/firebasejs/9.10.0/firebase-app-compat.js");
+importScripts("https://www.gstatic.com/firebasejs/9.10.0/firebase-messaging-compat.js");
+
+firebase.initializeApp({
+    apiKey: "...",
+    authDomain: "...",
+    databaseURL: "...",
+    projectId: "...",
+    storageBucket: "...",
+    messagingSenderId: "...",
+    appId: "...",
+});
+const messaging = firebase.messaging();

web/index.html

@@ -56,6 +56,7 @@
         // Wait for registration to finish before dropping the <script> tag.
         // Otherwise, the browser will load the script multiple times,
         // potentially different versions.
+        navigator.serviceWorker.register('firebase-messaging-sw.js');
         var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion;
         navigator.serviceWorker.register(serviceWorkerUrl)
           .then((reg) => {