Add COLR/CPAL and CBDT/CBLC color emoji support

[jspears]

Summary

Adds support for two additional color emoji font formats, building on the SBIX support in #1690.

Depends on #1690 — This PR is stacked on the SBIX emoji rendering PR. Once #1690 is merged, the diff here will shrink to only the COLR/CPAL and CBDT/CBLC changes.

COLR/CPAL (Vector Emoji)

• _renderCOLREmoji() — Renders COLR glyphs by iterating color layers, setting fill colors from the CPAL palette, converting path commands (including quadratic→cubic bezier conversion) to PDF operators.
• Tested with Twemoji.Mozilla.ttf.

CBDT/CBLC (Bitmap Emoji — Google Noto Color Emoji)

• _extractCBDTBitmap() — Navigates the CBLC strike index to find the best bitmap size, looks up glyph offsets via IndexSubtable (versions 1-5), and reads raw PNG data from CBDT (formats 17, 18, 19).
• _calcGlyphOffsetInCBDT() — Computes glyph offsets from fontkit's parsed subtable data.
• _manualCBLCLookup() — Fallback that manually parses raw CBLC binary data when fontkit's parser doesn't cover the target glyph.
• _emojiFragmentFallback() — Graceful degradation for fonts where fontkit's layout() fails (e.g., NotoColorEmoji). Uses _cmapProcessor.lookup() per codepoint and extracts CBDT bitmaps directly. Should work with PR fontkit pr 366
• Tested with NotoColorEmoji.ttf.

Routing

• _emojiFragment() updated to route based on glyph.type: COLR → vector rendering, else → bitmap (SBIX or CBDT fallback).
• Try-catch wrapper with fallback to _emojiFragmentFallback() for fonts where layout() crashes.

Bug Fixes

• Fill color reset after COLR rendering — pdfjs-dist 2.16.105 doesn't fully restore color space after Q (graphics state pop). Explicit fill color reset ensures subsequent text renders correctly.
• NotoColorEmoji layout crash — fontkit's getGlyph() returns null for CBDT-only fonts. Added try-catch in both _emojiWidthOfString and _emojiFragment with fallback paths.

Tests

• 34 mock-based unit tests covering _calcGlyphOffsetInCBDT, _extractCBDTBitmap, _manualCBLCLookup, _getEmojiImage, _emojiFragment, and _renderCOLREmoji.
• Real-font integration tests using Twemoji.Mozilla.ttf (COLR/CPAL) and NotoColorEmoji.ttf (CBDT/CBLC).
• Visual snapshot tests for COLR rendering (Twemoji), CBDT rendering (NotoColorEmoji), and SBIX rendering (Apple Color Emoji, conditionally on macOS).
• All 407 tests pass (54 suites, 87 snapshots).

Usage

import PDFDocument from 'pdfkit';

// COLR/CPAL font (e.g., Twemoji)
const doc = new PDFDocument({
  emojiFont: 'path/to/Twemoji.Mozilla.ttf',
  emojiFontFamily: 'TwemojiMozilla',
});

// CBDT/CBLC font (e.g., Noto Color Emoji)
const doc2 = new PDFDocument({
  emojiFont: 'path/to/NotoColorEmoji.ttf',
  emojiFontFamily: 'NotoColorEmoji',
});

doc.font('Helvetica').fontSize(18)
   .text('Hello 😀 World 🎉 from PDFKit');

Limitations

• ZWJ sequences in CBDT-only fonts (NotoColorEmoji) render as individual component emoji rather than composed glyphs, since fontkit's GSUB shaping doesn't work for these fonts.
• COLR v1 (gradient layers) is not yet supported — only COLR v0 (solid color layers).

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Pull Request opened by Augment Code with guidance from the PR author