feat(core)!: support string in rule that returns array

[chu121su12]

Closes #1092.

This PR expanded support for rule to return string inside an array.
The (somewhat) breaking change is that string-returned value will now be sorted among the same token.

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[antfu]

This seems not correct 🤔

[chu121su12]

This is the breaking change noted above. The result was swapped with its second result to its bottom.

That particular rule is based on string return, so it will not have selector in StringifiedUtil hence now sorted by its body. Before this PR this condition is not checked and returned as is as css value. That portion of rule start with the captured token used as selector:

unocss/test/preset-attributify.test.ts

Lines 87 to 91 in 0c861eb

	[/^custom-(\d+)$/, ([_, value], { rawSelector }) => {
	// return a string instead of an object
	const selector = e(rawSelector)
	return `
	${selector} {

The string to extract was <div custom="1" class="custom-2"> yielding [custom~="1"] and .custom-2. Sorting them leads to . < [ hence the swapped result.