This transform scans entry points for struct parameters that contain
the num_workgroups builtin, and replace accesses to these members with
a value loaded from a uniform buffer.
This will be used by the HLSL backend to implement the num_workgroups
builtin.
Bug: tint:752
Change-Id: Iefab3b14af8a08a6135348fded368a06d932e915
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/63961
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>