Add GrPathUtils::calcCubicInverseTransposePowerBasisMatrix

Cleans up calc_inverse_transpose_power_basis_matrix and makes it
publicly visible.

Bug: skia:
Change-Id: I568c2b8518c74931962ece23ed07490e7e10e94b
Reviewed-on: https://skia-review.googlesource.com/39180
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
2 files changed