Add SkColorMatrix factories for SkYUVColorSpace

This lets clients access and use the same RGB to YUV matrices that we
use internally.

Inspired by https://crrev.com/c/3223983

Bug: skia:12545
Change-Id: I7f70f56e721819c3d33da447eff2e572b7774c51
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/461476
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
3 files changed