Adds the first type trait that checks that the equality operator is
defined for two types.
Bug: dawn:441
Change-Id: Ied80c5d876739272c07d513727a3ee709a721eab
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/35522
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
