experiments to speed up drawing 32bit images into 565

New (legacy style) blitters only coded for shaders (and very restricted blendmodes)

Bug: skia:
See https://buganizer.corp.google.com/issues/64884885

Change-Id: Ie2546093bfe1e670a825dfd9542d252d53732c40
Reviewed-on: https://skia-review.googlesource.com/54103
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Herb Derby <herb@google.com>
7 files changed