This reduces the size of the pipeline cache descriptor under 256 bytes.
Further improves the speed of cache query. Has the minor cost of
needing more state application during a new command buffer or render
pass.

Bug: angleproject:2522
Change-Id: I3d71e457a36084ac4748d04fe3c9bab4caad503c
Reviewed-on: https://chromium-review.googlesource.com/c/1316888
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>