This CL moves the Validate methods from the Resolver into a specific
Validator class used by the Resolver.
Bug: tint:1313
Change-Id: Ida21a0cc65f2679739c8499de7065ff8b58c4efc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/87150
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>