Restrict SkStrikeInterface to GPU and rename to SkStrikeForGPU

SkStrikeInterface has become more and more focused on support of the GPU
stack. Finishing this focus clears up some of the confusing parts of the
Bitmap code.

Remove use of SkStrikeInterface from the BitmapCode.

Change-Id: I18a50d3ec17d81fcbe55030a3a3ec7eeeba23497
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/244297
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
13 files changed