Stop using GrPixelConfig in Metal & Dawn's GrProgramDesc creation

In order to be able to create GrProgramDescs pre-flush we would like as little reliance on the GrRenderTarget as possible (also GrPixelConfig is going away).

Bug: skia:9455
Change-Id: Ie35c87758bb1ed97c99c6e9e130eaeb3355f4139
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/256457
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Robert Phillips <robertphillips@google.com>
16 files changed