This PR condenses the namespaces in the tint/writer/spirv folder.
Change-Id: Ibe1d241b4a3da3c031b431d4ed2a95f197678def
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86022
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>