This allows interface blocks in Metal to compile even if
`layout(binding=...)` is not specified. It will also be used in SPIR-V
in the followup CL, when an interface block is automatically synthesized
for top-level uniforms.
This CL also reorganizes the unit tests around uniforms a bit.
Change-Id: Ia898c536b454dda6f51677e232a8f6e6c3606022
Bug: skia:11225
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/360778
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
