Implement indirect stroking for conics

Just like for fills, we use the normal Wang's formula on the conic's
down-projected control points until we can formalize on a better
formula.

Bug: skia:10419
Change-Id: Ifd735534a2e793f79f4f5d5b7e7acf50db81fe5e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/341156
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Tyler Denniston <tdenniston@google.com>
13 files changed