Janic Duplessis 1658f36630 Improve z-index implementation on iOS
Summary:
This avoids reordering views because it created some bugs when the native hierarchy is different from the shadow views. This leverages `layer.zPosition` and takes z-index in consideration when we check what view should be the target of a touch.

**Test plan**
Tested that this fixes some layout issues that occurred when using sticky headers in the Expo home screen.
Closes https://github.com/facebook/react-native/pull/14011

Differential Revision: D5108437

Pulled By: shergin

fbshipit-source-id: 0abfe85666e9d236a190e6f54cdd5453cacfbcac
2017-05-28 21:45:32 -07:00
..
2017-05-12 18:07:49 -07:00