[analytics] suggested events does not allow extra params

[danielgomezrico]

On firebase analytics library, there are multiple methods for each suggested event like login, signUp, search, and that's cool, one thing that makes me think is that they only allow their attributes, and so if I want to add like "view from which this event was thrown" or any other custom attribute I just can't.

https://github.com/FirebaseExtended/flutterfire/blob/1e1f509469bff0746e0e802a2ca6560764998898/packages/firebase_analytics/firebase_analytics/lib/firebase_analytics.dart#L692-L694

Proposal idea:

1. Remove all of those methods and create constants for each param and attribute like the google sdk does.
2. Left just the custom logEvent function with a custom hash parameter, so we can build the attributes in any way we want.

This is logEvent:
https://github.com/FirebaseExtended/flutterfire/blob/1e1f509469bff0746e0e802a2ca6560764998898/packages/firebase_analytics/firebase_analytics/lib/firebase_analytics.dart#L29-L31