[fill-stroke] Missing miter-clip value in stroke-linejoin definition

The [line join shape](https://drafts.fxtf.org/fill-stroke/#line-join-shape) algorithm mentions `miter-clip` as a possible value for `stroke-linejoin` but that value does not appear in the definition of the [`stroke-linejoin`](https://drafts.fxtf.org/fill-stroke/#propdef-stroke-linejoin) property.

(The value exists in the definition in [SVG Strokes](https://svgwg.org/specs/strokes/#LineJoin))