Remove SkBitmapProcStateAutoMapper's overflow check

(follow-up to https://codereview.chromium.org/1642273002)

Add an optional SkPoint outparam, and relocate the overflow check to
the only client which needs it.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1650403002

Review URL: https://codereview.chromium.org/1650403002
2 files changed