feat: add WebCrypto SHA-256 and SIMD bitmap optimizations

[superstructor]

Implement hardware-accelerated performance enhancements for FreeType:

WebCrypto Integration (8x target speedup):

• Add ftweb-crypto.h/c for browser crypto.subtle API
• Hardware SHA-256 hashing for font cache keys
• Async JS bindings with ASYNCIFY support
• Software fallback for small data or missing WebCrypto

SIMD Bitmap Operations (4x target speedup):

• Add ftsimd.h/c using WebAssembly SIMD128 intrinsics
• Optimized FT_SIMD_Bitmap_Copy (16 bytes/iteration)
• Optimized FT_SIMD_Bitmap_Blend with alpha blending
• Integrated into FT_Bitmap_Copy for automatic acceleration

Build System Updates:

• Add WebCrypto/SIMD sources to meson.build
• Enable -msimd128 compiler flag
• Configure ASYNCIFY for async WebCrypto calls
• Add benchmark task to deno.json

Benchmarks:

• Create webcrypto-bench.ts for performance validation
• SHA-256: Target ≥8x speedup over software
• Bitmap copy: Target ≥4x speedup over memcpy
• Bitmap blend: Target ≥3x speedup over scalar

Performance-critical paths optimized:

• Font cache key generation (SHA-256)
• Glyph bitmap copying (rasterization)
• Anti-aliasing bitmap blending