We were missing an `UnwrapRef` when generating the return type, and
were generating invalid SPIR-V when the value being stored was a
reference. The auto-generated builtin tests only test with literal
values.
Fixed: tint:1573
Change-Id: If42280b3cc8ad3fba7355d333e02400c6db843fa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/92144
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Auto-Submit: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>