This reduces size of state descriptors and increase hashing performance.

Bug: angleproject:2634
Change-Id: Ida1a17a4fb30a053dafc82a3f7501b448e16e818
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2192570
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>