Find cubic KLM functionals directly

Find cubic KLM functionals directly

- Updates GrPathUtils to computes the KLM functionals directly instead
  of deriving them from their explicit values at the control points.
- Updates the utility to return these functionals as a matrix
  rather than an array of scalar values.
- Adds a benchmark for chopCubicAtLoopIntersection.

BUG=skia:

Change-Id: I97a9b5cf610d33e15c9af96b9d9a8eb4a94b1ca7
Reviewed-on: https://skia-review.googlesource.com/9951
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>