[native] Disable overscroll for RegistrationContainer on iOS
Summary: Android already disables overscroll when the content is smaller than the ScrollView. This diff makes iOS do the same.
Test Plan:
- Confirmed that iOS behaves as if there is no ScrollView when the content is smaller than the ScrollView
- Confirmed that no change was observed when the content is larger than the ScrollView (it remains scrollable) by adding more bullet points to the ConnectEthereum screen
Reviewers: ginsu, atul
Reviewed By: ginsu
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D7826