skvm sprite blitter

Two diffs,
    - image_scale_aligned, all over
    - savelayer_coverage, in bottom-right corner

I think maybe these are both working as intended?
image_scale_aligned is now much more snapped to pixels,
and the bottom-right corner of savelayer_coverage now
looks like the top-right, where previously it looked like
the bottom-left.  Looking on Gold it seems this new image
closely matches images marked positive.

In any case, probably things that can be followed up on
later if they should be different.  I don't see any major
logical flow flaw.

Change-Id: I4cb308a8e1afffefec2464ec0b6f399dae34639b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306308
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed