🚀 [firebase_messaging]: Add 'registetedServiceWorker' parameter to 'getToken' method to better support web background message

[davoutuk]

The JS version of the FirebaseMessaging 'getToken' method includes an optional 'registeredServiceWorker' parameter. This pararmeter is missing from the Flutter/DART equivalent class.

Having this extra parameter would better support the web app support for background message/notification handling.

[SelaseKay]

Could you provide the link to the api reference?

[SelaseKay]

Hi @davoutuk, thanks for the report. I've created a PR for this feature.