BufferQueue: Add NATIVE_WINDOW_BUFFER_AGE query

Adds a NATIVE_WINDOW_BUFFER_AGE query, which returns the age of the
contents of the most recently dequeued buffer as the number of frames
that have elapsed since it was last queued.

Change-Id: Ib6fd62945cb62d1e60133a65beee510363218a23
(cherry picked from commit 49f810c72df8d1d64128e376757079825c8decd4)