[csswg-drafts] [css-pseudo][css-lists] Allow counter-* in ::marker (#5265)

Loirooriol has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-pseudo][css-lists] Allow counter-* in ::marker ==
The ::marker pseudo-element can use

```css
::marker {
  content: counter(my-counter);
}
```

However, something like `counter-increment: my-counter` won't work since `counter-increment` doesn't apply to ::marker. Gotcha, it has to be set in the list item instead.

So I think [`counter-increment`](https://drafts.csswg.org/css-lists/#propdef-counter-increment), [`counter-set`](https://drafts.csswg.org/css-lists/#propdef-counter-set) and [`counter-reset`](https://drafts.csswg.org/css-lists/#counter-reset) should just apply. Counters don't affect layout so there doesn't seem to be any problem.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5265 using your GitHub account