ccpr: Draw curves in a single pass

Throws out the complicated MSAA curve corner shaders, and instead just
ramps coverage to zero at bloat vertices that fall outside the curve.

Updates SampleCCPRGeometry to better visualize this new geometry by
clearing to black and drawing with SkBlendMode::kPlus.

Bug: skia:
Change-Id: Ibe86cbc741d8b015127b10dd43e3b52e7cb35732
Reviewed-on: https://skia-review.googlesource.com/112626
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
12 files changed