This CL updates the WGSL parser to parse `default` as a case selector
value.
Bug: tint:1633
Change-Id: I57661d25924e36bec5c03f96399c557fb7bbf760
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/106382
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>