VNDK ANativeWindow API - step 2

The vndk API is a superset of the NDK API.
Prior to this, vendor would have access to
system/window.h which itself is a superset of
what they need, exposes too much of the internals.

With this change, system/window.h depends on
vndk/window.h which depends on
android/native_window.h

Test: compiled, booted Nexus 6P
Bug: 34453351
Change-Id: Iad7bf035143541843309437fe630cc603d96a76e