SoftLight with SkPMFloat

SSE speeds up about 4.5x over existing integer SSE,
NEON speeds up about 3x over serial integer code.

We expect 1-2 bit component diffs in the usual GMs.

Still guarded by SK_SUPPORT_LEGACY_XFERMODES,
which I'll now try to lift in Chrome.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/3e47d49b46b3ab62071218ef3dd44642c9713e04

CQ_EXTRA_TRYBOTS=client.skia:Test-ChromeOS-GCC-Daisy-CPU-NEON-Arm7-Debug-Trybot

Review URL: https://codereview.chromium.org/1221493002
2 files changed