Plumb GrTextureProxies down into emitSampler/addSampler

This is still pretty far away from this goal but, the goal here is to be able to create a program w/o requiring instantiated proxies.

Bug: skia:9455
Change-Id: I9526a3a737438c5331fef4a621be4786ef43c080
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247397
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
13 files changed