add support for keyboard animation meta

[justinmakaila]

Summary

This adds animation meta information to the useKeyboard hook to support implementing custom keyboard avoiding views. Solution adds a new state hook that is used to indicate the duration of the animation, whether the animation is active (defined as transitioning from willShow/Hide to didShow/Hide), and what the animation type is: show | hide.

Test Plan

What's required for testing (prerequisites)?

What are the steps to reproduce (after prerequisites)?

Compatibility

OS	Implemented
iOS	✅
Android	✅
Web	❌

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I updated the typed files (TS and Flow)
• I've created a snack to demonstrate the changes: LINK HERE