Summary:
The current AndroidView stipulates that the backing shadow node can't
be a FlatShadowNode. In some cases, however, we want to apply some of the same
logic (ex not adding NodeRegions, etc) to other ViewManagers that have a
FlatShadowNode backing (and that don't necessarily create a FlatViewGroup).
This commit renames AndroidView to NativeViewWrapper, and re-introduces
AndroidView as an interface, so that logic for padding, NodeRegions, etc can
be shared.
Differential Revision: D2942387
