Migrate SkRasterPipelineOp enum into a separate header.

The code itself is unchanged.

Change-Id: I9b193f42d57ab49fc8c958a3ebc7d8f5293277d9
Bug: skia:14042
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/630016
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Herb Derby <herb@google.com>
10 files changed