CCPR: Optimize Hull geometry

Conceptualizes hulls a as single entity, rather than a set of "wedges"
fanned around the midpoint. Optimizes GSImpl hulls to use less, better
triangles and not use the midpoint. This refactoring also paves the
way for VSImpl hulls.

Bug: skia:
Change-Id: I6a03c7b64811edfd1589f11a5d102e6ee56ea2d2
Reviewed-on: https://skia-review.googlesource.com/83962
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
9 files changed