Only expose isConvex on path publicly.

Subsequent CLs can work on combining convexity and direction

Bug: skia:10670
Change-Id: Ia44769ea88ffd99a56d4c6729a80a2044e790ec2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/313837
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
13 files changed