Function icu_properties::provider::names::normalize_char

fn normalize_char(ch: u8) -> Option<u8>

Normalize a character based on the “loose matching” described in PropertyValueAliases.txt, returning None for skippable characters

ICU has code for this (and during property lookup) which we emulate. In particular, ICU only does normalization within ASCII, which makes sense since character names seem to be only ASCII.