feat: add :state() pseudo-class support

[bencbradshaw]

Feat: Add support for state() pseudo-class

Fixes:
#1036

[Acknowledgements]
WIP PR

[external]
Addresses and Enables
lit/lit#5208 (comment)

Note for Chromium based browser versions 90-124:
:state() will be in the output
Those browsers will ignore it (unknown selector = no match)

[x] - Tests Added
[x] - All tests Passing
[x] - documentation updated if needed (not needed)

[Copilot]

Pull request overview

This pull request adds support for the CSS :state() pseudo-class, which is used for styling custom element states. The implementation enables web components to expose internal states that can be styled from outside the shadow DOM.

Changes:

• Added parsing and serialization support for the :state() pseudo-class in the selector parser
• Implemented browser compatibility tracking with appropriate version requirements, filtering out partial implementations from Chrome/Edge 90-124
• Added comprehensive test coverage including basic usage, nesting, and complex selector scenarios

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/selector.rs	Added :state() parsing, enum variant, CSS output, and compatibility feature mapping
src/lib.rs	Added comprehensive tests for :state() including minification and nesting scenarios
src/compat.rs	Added StatePseudoClass feature with browser version compatibility checks
scripts/build-prefixes.js	Added MDN data extraction for :state() with filtering of partial implementations

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[devongovett]

Thank you!

[jp-knj]

Thanks!