Add gpu implementation of SkAvoidXfermode
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1658623002

TBR=bsalomon@google.com

Committed: https://skia.googlesource.com/skia/+/15691a055db9b68c9b48f589e48d8a85888cf83f

Review URL: https://codereview.chromium.org/1658623002
6 files changed