build custom blitter for drawAtlas

- add uniform_color_dst stage
- add stageupdate option for shaders

More cases we could try to handle in the future:
- perspective (not hard)
- mipmaps (plumbing is there, need to re-call bitmapstate helper)

Before

  10025.60  	drawAtlas_3	8888
   6636.06  	drawAtlas_2	8888

After

   3566.18  	drawAtlas_3	8888
   2585.83 ?	drawAtlas_2	8888

Change-Id: I656231324c0390029f6d08941c4f9d11ccdb8e87
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233061
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
6 files changed