Constant icu_timezone::provider::names::NON_REGION_CITY_PREFIX

pub const NON_REGION_CITY_PREFIX: u8 = b'_';

IanaToBcp47MapV3’s trie cannot handle differently-cased prefixes, like Mexico/BajaSur`` and MET`.

Therefore, any ID that is not of the shape {region}/{city} gets prefixed with this character inside the trie.

During lookup, if the input is not of the shape {region}/{city}, the trie cursor has to be advanced over this byte.