[SVGDom] Add fill-rule support

[SVGDom] Add fill-rule support

There's a bit of friction with this attribute, because per spec it is
an inherited presentation attribute, but in Skia it is part of the
actual SkPath state.

So we must add some plumbing to SkSVGShape & friends to allow overriding
the fill type at render-time.

R=robertphillips@google.com,stephana@google.com

Change-Id: I9c926d653c6211beb3914bffac50d4349dbdd2c0
Reviewed-on: https://skia-review.googlesource.com/5415
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>