[svg] Initial mask plumbing

Introduce SkSVGMask and plumb related attributes.

Also consolidate the clip/mask/filter property types - they all support
the same values: <funciri>|none|inherit.

Bug: skia:10842
Change-Id: If45a75cccc19b84d6547237336fe5d562a85d594
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/353436
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Tyler Denniston <tdenniston@google.com>
12 files changed