https://www.w3.org/TR/SVG11/filters.html#LightSourceDefinitions
The three classes represent light source elements that will eventually
be used for feSpecularLighting and feDiffuseLighting. Currently they are
unused.
Also added the (currently unused) lighting-color presentation attribute.
Bug: skia:10841
Change-Id: Ic7824671662b8cd88cf627affc54173d5e881b7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/359557
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
