static ACCENT_DIGRAPHS: Map<&'static [u8], char>Expand description
2-byte digraphs as a compile-time perfect hash table. 110 entries,
&[u8] keys (the 2 ASCII bytes), char values. phf::Map::get is
O(1) and constant-comparison-bounded, replacing the 110-entry
linear scan that the old ACCENT_TABLE lookup used.