ImageWriter: create a thread for buffer detaching

Calling detachNextBuffer while producer/consumer sits in the same
process will cause a deadlock. Creating a thread shared by all
alive ImageWriter instances to detachBuffers.

Test: new CTS tests using TextureView + ImageWriter
Bug: 122740799
Change-Id: I6231c75b93aa862449831a050b376f978b459bed
1 file changed