perf: use Uint8Array bitmaps for faster tag ID lookups

[TrevorBurnham]

This PR replaces Set.has() lookups with Uint8Array bitmap lookups for tag ID membership checks in hot paths. Bitmap array indexing is ~3-4x faster than Set.has() for small integer keys, and TAG_ID values (0-120) are ideal candidates for this optimization.

This PR also adds benchmarks for SVG parsing. The effect of this change on those benchmarks is minimal, but they should be useful for preventing future performance regressions and testing other potential optimizations.

Changes

packages/parse5/lib/parser/open-element-stack.ts

• Replaced Set<$> with Uint8Array bitmaps for scope boundary checking:
  • SCOPING_ELEMENTS_HTML_BITMAP
  • SCOPING_ELEMENTS_HTML_LIST_BITMAP
  • SCOPING_ELEMENTS_HTML_BUTTON_BITMAP
  • SCOPING_ELEMENTS_MATHML_BITMAP
  • SCOPING_ELEMENTS_SVG_BITMAP
• Updated hasInDynamicScope() to use bitmap lookups instead of Set.has()

packages/parse5/lib/common/foreign-content.ts

• Replaced EXITS_FOREIGN_CONTENT Set with EXITS_FOREIGN_CONTENT_BITMAP Uint8Array
• Updated causesExit() to use bitmap lookup

bench/perf/svg-benchmark.js (new)

• Added comprehensive SVG parsing benchmark to test foreign content handling performance
• Tests various SVG patterns: simple shapes, paths, nested groups, attribute-heavy elements
• Compares SVG parsing performance against equivalent HTML complexity

Micro-benchmark Results

Set.has vs Bitmap lookup for tag ID membership:
  Set.has:   45.45ms
  Bitmap[]:  13.25ms
  Winner: Bitmap[] (3.43x faster)

End-to-End Benchmark Results

The bitmap optimization shows neutral to slightly positive results in end-to-end benchmarks (within margin of error).

Why This Approach

1. Zero runtime cost: Bitmaps are created once at module load time
2. Cache-friendly: Uint8Array is compact and fits in L1 cache
3. Simple indexing: bitmap[tagId] vs set.has(tagId) - direct array access vs hash lookup
4. No API changes: Internal optimization only, no breaking changes

[43081j]

makes sense to me! 👍

will wait for @fb55 to review too