Replace the hand-written accent map with letterFolds, a table generated
offline by gen_folds.py from Python's unicodedata: every code point whose
canonical decomposition contains combining marks maps to its base letters,
plus stroked Latin letters and ligatures. Combining marks are still dropped,
so composed and decomposed spellings ("Phở" and "Phở") now
normalize equal. No new dependency.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>