Move float<->byte conversions into Sk4f.
This lets us avoid conversions to [0.0, 1.0] space and rounding that aren't necessary
for SkColorCubeFilter_opts.h.
Dropping rounding on the way back to bytes means we'll see a bunch of off-by-1 diffs.
Rough perf effect:
SSSE3: 110 -> 93 (~15%)
NEON: 465 -> 375 (~20%)
This is the beginning of the end for SkPMFloat as an entity distinct from Sk4f.
I've kept it for now so I can convert sites one by one and think about how things
that really want to keep PM color order will work.
BUG=skia:4117
Review URL: https://codereview.chromium.org/1319413003
8 files changed