Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41051
Strictifies flow to flow strict-local in files where doing that doesn't cause new flow errors.
Changelog: Internal
Reviewed By: yungsters
Differential Revision: D50369011
fbshipit-source-id: b4a5a26b839b7327a3178e6f5b35246dea365a38