This CL updates the `workgroup_size` attribute to use `expression`
values instead of `primary_expression`.
Bug: tint:1633
Change-Id: I0afbabd8ee61943469f04a55d56f85920563e2da
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/99960
Reviewed-by: Ben Clayton <bclayton@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>