This allows them to be used in various places that WGSL allows, such
as function return types and parameters, and as the type of the RHS of
an assignment.
Fixed: tint:814
Fixed: tint:820
Change-Id: Idb6a901b9a34e96bb9733cc158191e7b3bafaa0e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/52844
Auto-Submit: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
James Price