Fix browser notification permission request logic (#13543)

* Add notification permission handling code

* Request notification permission when enabling any notification setting

* Add badge to notification settings when permissions insufficient

* Disable alerts by default, requesting permission and enable them on onboarding

app/javascript/mastodon/utils/notifications.js

@@ -0,0 +1,29 @@
+// Handles browser quirks, based on
+// https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API/Using_the_Notifications_API
+
+const checkNotificationPromise = () => {
+  try {
+    Notification.requestPermission().then();
+  } catch(e) {
+    return false;
+  }
+
+  return true;
+};
+
+const handlePermission = (permission, callback) => {
+  // Whatever the user answers, we make sure Chrome stores the information
+  if(!('permission' in Notification)) {
+    Notification.permission = permission;
+  }
+
+  callback(Notification.permission);
+};
+
+export const requestNotificationPermission = (callback) => {
+  if (checkNotificationPromise()) {
+    Notification.requestPermission().then((permission) => handlePermission(permission, callback));
+  } else {
+    Notification.requestPermission((permission) => handlePermission(permission, callback));
+  }
+};