This packs the desc into 288 bytes. Down from over 400. The hashing and
memcmp functions are sped up considerably.

Improves performance in the VulkanPipelineCachePerf test by 50% and
also improves performance in the state changing draw call test by 20%.

Bug: angleproject:2522
Change-Id: I72ed191a93721b875684f647f806c09be4e66821
Reviewed-on: https://chromium-review.googlesource.com/c/1308460Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>