Add a failing test case for & within a nested function in a declaration value

[Andarist]

Related to emotion-js/emotion#2943

[Andarist]

\f gets incorrectly appended to & here:

stylis/src/Parser.js

Lines 47 to 49 in bc0b1b0

	if (indexof(characters += replace(delimit(character), '&', '&\f'), '&\f') != -1)
	ampersand = -1
	break

I'd like to conditionally use this replace here - we need to skip it when we are in the context of the property. I've tried to use property for this and while I managed to fix this case I broke some other cases like this one:

stylis/test/Parser.js

Lines 593 to 601 in bc0b1b0

	test('pseudo-selector with & in a string', () => {
	expect(
	stylis(`
	h1:matches(&,[href="https://css-tricks.com?a=1&b=2"]) {
	display: none
	}
	`)
	).to.equal(`h1:matches(.user,[href="https://css-tricks.com?a=1&b=2"]){display:none;}`)
	})

[Andarist]

@thysultan friendly 🏓

[github-actions]

Pull Request Test Coverage Report for Build 673315f00359b3ae65949786d475d88332f8149d-PR-307

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 98.849%

---

Totals
Change from base Build bc0b1b03f5562eb8b38601e4e05461631a91c400:	0.006%
Covered Lines:	271
Relevant Lines:	273

---

💛 - Coveralls

[thysultan]

@Andarist didn't notice this when you opened it, (only the friendly ping): fixed in the head commit, you can merge/release this one.

[coveralls]

Pull Request Test Coverage Report for Build 673315f00359b3ae65949786d475d88332f8149d-PR-307

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 98.849%

---

Totals
Change from base Build bc0b1b03f5562eb8b38601e4e05461631a91c400:	0.006%
Covered Lines:	271
Relevant Lines:	273

---

💛 - Coveralls