Summary:
This diff adds support for value offsets on iOS. It separates out code originally submitted in #9048.
Test plan (required)
Set up an animation with an offset, and `useNativeModule: true`. Compare results with `useNativeModule: false`.
Closes https://github.com/facebook/react-native/pull/9627
Differential Revision: D3924410
fbshipit-source-id: 8177a25a5f6b9e33f00ea66143c782aeea24507d