Constant icu_datetime::fields::length::FIRST_NUMERIC_OVERRIDE

const FIRST_NUMERIC_OVERRIDE: u8 = 17;

First index used for numeric overrides in compact FieldLength representation

Currently 17 due to decision in https://unicode-org.atlassian.net/browse/CLDR-17217, may become 16 if the > 16 is updated to a >= 16