Summary:
`UITextField` don't have delegate to observe the selection changes of users(multiline text input `UITextView` have it), so we can add a KVO to observe selection changes.
cpojer shergin
[iOS] [Fixed] - Fixes selection of single line text input
Pull Request resolved: https://github.com/facebook/react-native/pull/24714
Differential Revision: D15238379
Pulled By: cpojer
fbshipit-source-id: f149721d6b4df28e90f5a9405c74e01fde7c7d10