RN: Flowify `packages/react-native` Mocks & Tests (#51794)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51794

Adds `flow` to the remaining mocks and tests that are lacking it in the `packages/react-native` directory.

This required adding numerous type annotations and suppressions.

Changelog:
[Internal]

Reviewed By: javache

Differential Revision: D75930095

fbshipit-source-id: ebb1280adc656680e00fd579701e31521826b55c