add _sRGB 8888 formats

Trickiest bits were remembering which side gets _Inverse_,
and ensuring our test scenarios always run all transform steps.

Change-Id: Ib4acfa097eb0e9213c27777828026a1f1f9ac015
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/278800
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed