Implement gradient ramp using SG shader effects.
A couple of quirks:
- since the gradient type (linear/radial) is animatiable (?!),
update sksg::ShaderEffect to allow resetting the shader
- gradient ramp doesn't have an assigned/stable JSON effect type,
but the data is present; introduce a name-based effect lookup method
(used as a fallback when the type is not recognized)
Change-Id: I02bbd6c75c3af175b64c1df502aa52b7c0875162
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205342
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
3d846c98ca