[svgdevice] Add support for color shaders

Handle kColor_GradientType (which is returned by asGradient
for color shaders) as a straight color paint server.

Bug: skia:12622
Change-Id: I46fa21ed23a7824d67fc0460f92d649743e1b1f2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/469900
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Tyler Denniston <tdenniston@google.com>
2 files changed