[canvaskit] Add isPointInPath / isPointInStroke

While working on this, I realized some things I did
caused winding to be inconsistent with what the Canvas
spec said (and with what Chrome did).

This CL includes 2 changes to remedy that:
 - removal of the subpath (which added needless complication).
 - re-write of ellipse() (to mirror Chrome's implementation).

Bug: skia:
Change-Id: Idd6c8a40b3c46598892e50a1e586f2ff66b801e3
Reviewed-on: https://skia-review.googlesource.com/c/175425
Reviewed-by: Florin Malita <fmalita@chromium.org>
8 files changed