1747 [cloud_functions] Remove unused header reference (cla: yes)

1748 Auto retrieve version to report user agent (cla: yes)

1749 re-add deleted files (cla: yes)

1750 [firebase_crashlytics][ios] setUserIdentifier incorrectly calls setUserEmail (cla: yes)

1751 [in_app_purchase] Fixed code example error & README links  (cla: yes, documentation, submit queue)

1753 [share] Add subject as optional parameter (cla: yes)

1756 [firebase_messaging] fix crash when func deleteInstanceID return result in incorrect thread (cla: no, flutterfire)

1758 [firebase_ml_vision] Move firebase_ml_vision examples to this repo (cla: yes, flutterfire)