Support comma operator with mixed types in SPIR-V.

Change-Id: Iac8096f6c225258b430858bad90199ec00b93b6c
Bug: skia:10998
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/342304
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed