Fix instances where hwaa was wrong for mixed samples

Fixes a bug with coverage-AA hairlines where hwaa was unintentionally
enabled for mixed samples, and a bug with path stenciling where hwaa
was unintentionally disabled for mixed samples.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2043203004

Review-Url: https://codereview.chromium.org/2043203004
2 files changed