Summary:
part of #24875. iOS only it appears, but not really used by RN itself. Should be fine?
## Changelog
[General] [Added] - Add TM spec for KeyboardObserver
Pull Request resolved: https://github.com/facebook/react-native/pull/24881
Reviewed By: fkgozali
Differential Revision: D15391769
Pulled By: rickhanlonii
fbshipit-source-id: 557507f6063b40d1c68ec8739e23b33bc22ade39