Add private GrContext::compile API (take 2)

Currently this is only implemented for GL.

Bug: skia:9455
Change-Id: I851471d6334d6a38e6fde3a46f09b7dc0209fb78
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272346
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
16 files changed