Summary:
Changelog: [iOS][Internal] - add x/y & pageX/Y implementations to PointerEvent interface
This diff adds the x/y properties, which are defined as aliases of clientX/clientY respectively. In addition this diff adds pageX/pageY which, while not definted as aliases of clientX/clientY, are effectively aliases in React Native since the root view is not scrollable (client and page points only differ on the web when a user has scrolled the document element).
Reviewed By: lunaleaps
Differential Revision: D37766818
fbshipit-source-id: c7ad3750460b1913889c6d1a55b4c1edc6918f5b