Move Wang's formula back into src/gpu/tessellate

We are making src/gpu/tessellate independent of v1, and more represent
math and types that just know how to tessellate, so this seems like the
right place again for this file.

Bug: skia:12524
Change-Id: I773de3c0f93a57ce7ee16b44480667013f32ebd5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459136
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
13 files changed