function getAlternateCodes(code) {
    if (alternateCharsCache.has(code)) {
        return alternateCharsCache.get(code);
    }
    // NOTE: This function is written in such a way that it can be extended in
    // the future, but right now the return type takes into account it's only
    // supported by a single "alt codes provider".
    // `ArrayLike<ArrayLike<number>>` is a more appropriate type if changed.
    let result;
    const codes = getKoreanAltChars(code);
    if (codes) {
        result = codes;
    }
    alternateCharsCache.set(code, result);
    return result;
}
Gets alternative codes to the character code passed in. This comes in the
form of an array of character codes, all of which must match _in order_ to
successfully match.

@param code The character code to check.