use reversePathTo in place of addPathReverse

use reversePathTo in place of addPathReverse

Path ops was using addPathReverse, instead of reversePathTo.
The former adds a moveTo always, and the latter requires
that the caller add the moveTo if needed.

Simplify the reversePathTo implementation.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2481463002

Committed: https://skia.googlesource.com/skia/+/d8db392be9dd1887df04b10b5670991d6b098c17
Review-Url: https://codereview.chromium.org/2481463002