[WIP] feat(swc/parser): multiple nesting selector

[alexander-akait]

Description:

Allow to parse:

.foo {
  color: blue;
  && { padding: 2ch; }
}

Ref: https://www.w3.org/TR/css-nesting-1/#nesting

BREAKING CHANGE:

Maybe

Related issue (if exists):

@tabatkins Hello and sorry for ping, we need your advice and help here. In spec we have:

The nesting selector is allowed anywhere in a compound selector, even before a type selector, violating the normal restrictions on ordering within a compound selector.

But if you look at https://www.w3.org/TR/selectors-4/#grammar

Compound selector contains a lot of other selectors, so based on the condition above, we can get (and it looks weird):

.class {
   &div#id:pseudo-class&::pseudo-element& { }
}

So can you provide syntax of <compound-selector> with <nesting-selector> to fully undestand syntax and will be great to have it in spec too, thank you