Add comprehensive text rendering test page for fixtures

[Copilot]

This PR adds a comprehensive HTML test page specifically designed to test various text rendering features in the JSAR Runtime. The new fixtures/html/text-rendering-test.html file provides extensive coverage of text-related CSS properties and rendering scenarios.

Features Tested

The test page includes 15 comprehensive sections covering:

Core Text Properties:

• Text Alignment: left, center, right, justify
• Line Height: normal, numeric values (1, 1.5, 2), pixel values (30px), percentages (150%)
• Font Families: serif, sans-serif, monospace, cursive, fantasy, and specific fonts (Arial, Times New Roman, Courier New)
• Font Sizes: Various units including px (12-32px), em (1-2em), rem, and percentages
• Font Weights: normal, bold, lighter, bolder, and numeric values (100-900)
• Font Styles: normal, italic, oblique

Advanced Text Features:

• Text Decorations: underline, overline, line-through, and combinations
• Text Transforms: uppercase, lowercase, capitalize
• Letter/Word Spacing: normal, positive, and negative values
• White Space Handling: normal, nowrap, pre, pre-wrap, pre-line
• Text Overflow: clip and ellipsis behaviors
• Vertical Alignment: baseline, top, middle, bottom, super, sub

Complex Text Scenarios:

• Multilingual Content: English, Chinese, Arabic, Russian, Japanese, Korean, French, Spanish, Portuguese, German, Italian
• Special Characters: Emoji, mathematical symbols, punctuation
• Text Effects: shadows, directional text (LTR/RTL)
• Performance Testing: Large text content for stress testing

Interactive Features

The page includes interactive functionality for testing:

• Hover effects on sections for visual feedback
• Click-to-copy functionality for CSS properties
• Dynamic content generation for performance testing
• Console logging for debugging and validation

Implementation Details

• 758 lines of comprehensive test content
• 80+ individual test cases across 15 major categories
• Bilingual labels (Chinese/English) for international testing
• Consistent styling following existing fixture patterns
• Responsive design with proper viewport meta tags
• Semantic HTML structure with proper accessibility considerations

This test page will be valuable for:

• Validating text rendering engine functionality
• Testing CSS text property implementations
• Performance testing with various text content types
• International text rendering validation
• Debugging text layout and styling issues

The file follows the established patterns in the fixtures/html directory and is now the most comprehensive text testing fixture available in the project.

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