SkSL version of color conversion functions for new CSS gradients

Not used yet. These are direct (ie slow) translations of the reference
transformations in the spec.

Bug: skia:13108
Change-Id: Iaf29607f18e1d90485497ce1ff707dd6587d4300
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/583858
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
3 files changed