A new FirebaseCrashlytics method that returns instance by given name

[ndnam198]

Please refer this question for detailed information:
#11183

[ndnam198]

For now, FirebaseCrashlytics.instance only returns an instance for the default name: "[DEFAULT]", if I create FirebaseApp with a customized name, let's say "MyFirebaseApp", then there aren't any ways to get FirebaseCrashlytics of that new instance.

FirebaseAnalytics.instanceFor is an exact example of what I want