Similar to the handling of packed values in the arithmetic operators
the shift operators need to cast to the unpacked type before doing the
as_type casts.
Bug: tint:1542
Change-Id: I4289c45ab0a067ce122f61675fe5e251a83b6f8b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/105720
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
d5139b4463