Improve handling of cusps in GrStrokeTessellateOp

Takes more care when chopping to make sure cusps are detected and
handled correctly.

Bug: skia:10419
Change-Id: I11f1c31534b3266155e9b47eb0daa5bd676fe2a6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/365817
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
4 files changed