fix pathops stitching bug

Tight data generates intersections that are currently
unsortable. Edges that can be sorted are added; simple
connected edges need to be added as well.

Look for output edges with gaps and add simple edges that
continue at the ends to reduce the gap size.

Extended tests with region check (pathops_unittest -V -x)
pass in debug and release.

TBR=reed@google.com

Bug: skia:8223
Change-Id: Ib0f22061ae3676e1a3b94574516a61cbbea2948f
Reviewed-on: https://skia-review.googlesource.com/145644
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
6 files changed