Summary:
This PR tries to remove the code duplication between `RNTesterApp.ios.js` and `RNTesterApp.android.js`. The common code has been moved to `RNTesterAppShared.js`.
This PR also refactors the state architecture and simplifies it to use just one single `useReducer` hook to manage the app's state.
It also adds the visibility hack to make the screen change a little bit faster and removed the unneeded test files.
Pull Request resolved: https://github.com/facebook/react-native/pull/29777
Reviewed By: cpojer
Differential Revision: D23349302
Pulled By: rickhanlonii
fbshipit-source-id: ce0d7b03e6ef65b1655bcb744817b73c5144438b
