This prevents later issues with some VkFormat values being over 256,
as well as providing more information to pipeline creation.
A preliminary step towards handling mismatched vertex attributes.

Bug: angleproject:3634
Change-Id: Idb15a14088a2d73b43b4b92d3cfdb12587c5f711
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1696212Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>