[IOS] [BUGFIX] [MESSAGING] fix getToken() always returning initialToken (#1510)
[ANDROID] [NOTICE] [MESSAGING] deprecate RNFirebaseInstanceIdService in favour of FirebaseMessagingService's onNewToken event. Remove this service from your AndroidManifest.xml
[IOS] [ANDROID] [INTERNAL] [MESSAGING] getToken & deleteToken now use Firebase InstanceID token management apis (with an FCM scope).
Add more tests for Realtime Database
### Summary
Increases test coverage, which should be helpful when starting work on v6.
### Checklist
- [x] `e2e` tests added or updated in [/tests/e2e/\*](/tests/e2e)
### Release Plan
[TESTING][ENHANCEMENT][Database] - More tests
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* [internals][js] nativeWithArgs wrapper incorrectly wrapping NativeModule constants - should only wrap functions
* [ios][android][js][auth] ensure user login state is consistent across RN reloads + tests
* remove test focus
* [android][auth] clear all auth state and id token listeners between React Native reloads
* [ios][auth] clear all auth state and id token listeners between React Native reloads
* [ios][auth] cleanup and add new auth error codes
- [ANDROID] [BUGFIX] [DATABASE] - Database listeners now correctly tearing down between RN reloads. (Fixes#1498#1611#1609)
- [JS] [BUGFIX] [DATABASE] - Fixed an issue where `Reference.toString()` incorrectly contains `//` instead of `/` when joining the parent and child paths.
- [JS] [BUGFIX] [DATABASE] - Rework `.push()` behaviour to match WebSDK and correctly return a Reference instance in all scenarios. (Fixes#893#1464#1572)
- [JS] [ENHANCEMENT] [UTILS] - Added a `firebase.utils().database.cleanup()` utility method which removes all database listeners.
solves: #1591 using the first solution:
> 1. Still consider the invocation a success, providing downloadURL as null.
Can some maintainer help me with the new test case? I need a file with permission to upload but not to download.
