Support universal selector (*) in CSSOM selector parser and matching

[Copilot]

This PR implements support for the universal selector (*) in the CSSOM selector parser and matching implementation, addressing a core CSS feature that was missing from JSAR's CSS processing.

What's Changed

The universal selector (*) is a fundamental CSS selector that matches any element. This implementation adds complete support for parsing and matching universal selectors in all contexts:

/* Basic universal selector */
* { color: red; }

/* Compound selectors with universal */
*.class { background: blue; }
*#myid { font-size: 16px; }

/* Combinators with universal */
div * { margin: 10px; }
section > * { padding: 5px; }
h1 + * { border-top: 1px solid; }

/* Pseudo-classes with universal */
*:hover { cursor: pointer; }
*:focus { outline: 2px solid blue; }

Implementation Details

The changes follow the existing codebase patterns and are minimal:

1. Added ComponentType::kUniversal to the component type enum
2. Added isUniversal() method to the Component class for type checking
3. Enhanced parseComponent() to recognize and parse the * character
4. Updated matching logic so universal selectors match any element (always return true)
5. Added string representation for universal selectors in serialization

Testing

Comprehensive test coverage includes:

• Basic universal selector parsing and matching
• Compound selectors combining universal with classes, IDs, and pseudo-classes
• Universal selectors with all combinator types (descendant, child, sibling)
• Multiple selector lists containing universal selectors
• String representation validation
• Visual HTML test fixture at fixtures/html/universal-selector-test.html demonstrating all features

All changes maintain backward compatibility and pass existing formatting checks.

Fixes #260.

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[yorkie]

@copilot Add a html at fixtures/html to test this feature

[Copilot]

@copilot Add a html at fixtures/html to test this feature

Added comprehensive HTML test file at fixtures/html/universal-selector-test.html that demonstrates all universal selector features including basic usage, compound selectors, combinators, pseudo-classes, and edge cases. The test file provides visual validation of the universal selector implementation. (6ed75f9)