[css-pseudo] highlight pseudos and compat stroke/fill properties #7580

https://drafts.csswg.org/css-pseudo-4/#highlight-styling

The following properties apply to the highlight pseudo-elements:

• […]
• stroke-color, fill-color, and stroke-width

‘-webkit-text-fill-color’, ‘-webkit-text-stroke-color’, ‘-webkit-text-stroke-width’, and ‘-webkit-text-stroke’ are unrelated to those SVG-only properties, but they work roughly the same way and are supported interoperably. WPT even has a test for ::selection with ‘-webkit-text-fill-color’. Should we make these properties applicable to highlights?

(@fantasai, @frivoal, @mrego)