support pseudo-class function which contains less `Variable` or other edge case

Here are 2 examples of valid code using the :is pseudo-class that are not handled by LESS correctly. Can you please allow valid code like this to work with LESS?

Tested on: https://lesscss.org/less-preview/
which erroneously issues the error message: Missing closing ')' for both examples.

@-moz-document domain("example.com") {
	:is([foo], [bar] /* :is(a, b) */, [baz]) {
		color: red; }
}

@-moz-document domain("example.com") {
		:is(
			[a1],
			[a2]
		):is(
			[a3],
			[a4]:not(
				:is([a5],[a6])
			):is(
				[a7]:not(:is([a8],[a9])),
				[b1]:not(:is([b2],[b3]))
			):is(
				[b4],[b5]
			),
			[b6],
			[b7]
		) {
			color: red; }
	
}

See also: https://github.com/openstyles/stylus/issues/1253