feat: Add support for most CSS nesting rules

[nzakas]

This pull request implements parsing for most CSS nesting rules. This works for rules beginning with:

• Universal selector
• Attribute selector
• Class name selector
• ID selector
• Pseudoclass/pseudoelement selector

The only I couldn't figure out is the element selector. I've also pushed these changes to csstree#337 in the hopes to get some feedback on how to do that.

In the meantime, I don't want to hold up getting these changes merged in.

Expansion of test cases for nested CSS rules:

• Replaced the test case for invalid nested rules with new cases for valid nested selectors, including class, ID, attribute, universal, and pseudoclass selectors in fixtures/ast/rule/nesting.json. These updates ensure the parser correctly handles a broader range of nested selectors. [1] [2] [3]

Parsing logic updates:

• Added new token types (Delim, Hash, Colon, LeftSquareBracket) and a selectorStarts set to identify valid selector starting characters in lib/syntax/node/Block.js.
• Updated the consumeDeclaration function to include a helper method isSelectorStart, which checks for valid selector starting tokens.
• Modified the parse function to use isSelectorStart for determining whether to consume a rule, enabling support for more selector types.

[coveralls]

Pull Request Test Coverage Report for Build 14574924483

Details

• 19 of 19 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 98.6%

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Totals
Change from base Build 14558259965:	0.002%
Covered Lines:	11718
Relevant Lines:	11850

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💛 - Coveralls

[fasttime]

Enhancements to CSS property handling:

* Added support for `overflow-x` and `overflow-y` properties with vendor-specific keywords in `data/patch.json`.

* Introduced the `position-try-options` property to support fallback strategies for CSS positioning.

I don't see any changes in data/patch.json. Maybe you forgot to commit the file?

[nzakas]

It got updated on main before this, so when I rebased that file disappeared.

[fasttime]

Ah, I see!

[fasttime]

LGTM, thanks!