Summary:
LegacyViewManagerInterop layer can now handle events as well.
We expose `eventInterceptor` from `NSComponentData`, that way we can hook into event dispatching that happens within `NSComponentData`.
Coordinator has a map of `UIView -> reactTag` which it uses to figure out to which component view to forward the event.
New `LegacyViewManagerInteropViewEventEmitter` exposes APIs to send `folly::dynamic` to javascript.
Reviewed By: shergin
Differential Revision: D17765834
fbshipit-source-id: 25e75e445b32c69ec9ab0189c4ab7fba5f8c7b5d