Overhual DvrBuffer and DvrBufferQueue API: Step 1

Adding new APIs:

dvrWriteBufferQueueGainBuffer
dvrWriteBufferQueuePostBuffer
dvrReadBufferQueueAcquireBuffer
dvrReadBufferQueueReleaseBuffer

Those new APIs streamlines DVR buffer operations:
1/ It allows static Dvr{Read,Write}Buffer objects to be statically
allocated with the queue.
2/ Symentric Gain/Post on WriteBufferQueue and Acquire/Release on
ReadBufferQueue.
3/ Use fixed buffer metadata.
4/ This is also a prerequisite to using shared memory based metadata and
async buffer IPC.

More details and discussion at: go/gvr-async-bufferhub

Special note regarding DVR API order in this CL: The new buffer queue
API entries are inserted before new PoseClient API as the PoseClient is
still blocked from being released and the new BufferQueue APIs are
expected to be released sooner than that.

Bug: 65455724
Bug: 65468551
Bug: 65458332
Bug: 65165821
Test: dvr_api-test
Change-Id: Iae8e7787d696d72ebf7457df9f98f4467cd20932