Add SkSL::ShaderCaps and use as base class for GrShaderCaps

Bug: skia:12559
Change-Id: I76b225c9ca81264a15869324007d774d210053b5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/473416
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
23 files changed