Add atan2_ primitive to SkRasterPipeline.

This logic is also adapted directly from SkVM.

Change-Id: I0b8960fb79511fab3cdad826af4439d1e8d2cb31
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/635616
Reviewed-by: Herb Derby <herb@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
3 files changed