bugfix: Classes that contain :is or :where in their names are no longer unintentionally purged

[AdrianGonz97]

Proposed changes

Class selectors that contained :is or :where within their names were being unintentionally purged. The use-case that brought about this issue was using these pseudo-classes in tailwind (e.g. class="[&:where(.some-class)]:text-black"), which would generate the following CSS:

.\[\&\:where\(\.some-class\)\]\:text-black:where(.some-class) {
	color: black;
}

This regex will misfire for the class above and for any classes that contain :where or :is in their names (even when the class name is added to the safelist!):

if ( selector.toString() && /(:where$)|(:is$)|(:where[^(])|(:is[^(])/.test(selector.toString()) ) {
	selector.remove();
}

As such, I added the appropriate tests, slightly widened the regex and added a more rigorous check for if the functional pseudo-class is empty of selectors:

if ( selector.toString() && /(:where)|(:is)/.test(selector.toString()) ) {
	selector.walk((node) => {
		if (node.type !== "pseudo") return;
		if (node.value !== ":where" && node.value !== ":is") return;
		if (node.nodes.length === 0) {
		  selector.remove();
		}
	});
}

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[AdrianGonz97]

Note: This was added to the safelist as the default extractor doesn't properly extract the whole class name.