Add support for svg fill-rule

[mroeling]

https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/fill-rule

Although candidate recommendation in SVG 2, it seems to work in current versions of Chrome (83.0.4103.116) and Firefox DeveloperEdition (78.0b9).

[Ugoku]

fill-rule already existed in SVG 1.1: https://www.w3.org/TR/SVG11/painting.html#FillRuleProperty
I expect full support in all browsers that support SVG

[GPHemsley]

This is ostensibly covered by MDN data (via mdn/browser-compat-data#1627), but it is currently empty:
https://github.com/mdn/browser-compat-data/blob/0d67d44dfd3f11b8b1ea31803df68e5456509971/svg/attributes/presentation.json#L852-L900

I imagine the MDN repo would greatly appreciate a PR to fill that in.

Side note: the SVG 1.1 and SVG 2 definitions appear to be substantially similar.
https://svgwg.org/svg2-draft/painting.html#FillRuleProperty