Add GrWangsFormula implementation for conics

Also add a unit test that the vectorized version equals the reference
implementation.

Bug: skia:10419
Change-Id: I4d165fd45532e9ec468565d0637fb769b51f5fcd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/345122
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
3 files changed