Implement gradient color space options in SkVM
Implement gradient color space options in SkVM

We'll want an SkRasterPipeline version eventually, but this was
straightforward, and ensures that the new features always have a
working fallback (eg, if the paint also includes SkSL).

This is a direct implementation of the conversion functions from the
CSS specification. We'll be optimizing all of these to remove
unnecessary steps soon.

Bug: skia:13108
Change-Id: Ib70ec5bc2a5c12445a4a16c676bf2075b68f66f1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/595757
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia