onMessageOpenedApp property Null safety
Returns a Stream that is called when a user presses a notification message displayed via FCM.
A Stream event will be sent if the app has opened from a background state (not terminated).
If your app is opened via a notification whilst the app is terminated, see getInitialMessage.
static Stream<RemoteMessage> get onMessageOpenedApp => FirebaseMessagingPlatform.onMessageOpenedApp.stream;