No need for the HLSL-style repeated swizzle; GLSL allows construction
of a vector from a scalar value of the component type.
Bug: tint:1317
Change-Id: Ia0afe3012cbb56716a2d1c5c3849dd662a5ff89c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/70342
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>