[firebase_auth] Fixes completely broken reauthenticateWithCredential method.

[slightfoot]

IGNORE THIS PR - Duplicate #237

Description

Last November there was a move away from the methods for each auth provider and to instead use the new credential methods. #928 c78ced7 At this point the reauthenticateWithCredential dart method invoked the platform channel and did not expect any response data.

Along came #1911 cc7353b in July where all the auth methods were set to return a AuthResult object. However, nobody updated the platform specific code for reauthenticateWithCredential to return back the fields for AuthResult. This has left the reauthenticateWithCredential method in dart broken since then.

This PR fixes the platform specific code to account for this change.

Related Issues

• Caused by [firebase_messaging] Both onMessage and onLaunch called with same gcm.message_id #1911 cc7353b
• Fixes [firebase auth] FirebaseUser.reauthenticateWithCredential finished with NoSuchMethodError exception #76

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• If the pull request affects only one plugin, the PR title starts with the name of the plugin in brackets (e.g. [cloud_firestore])
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[slightfoot]

Looks like PR has already been submitted. Whoops. Closing because handled already by #237.