Function utf32to8

third-party/utf8cpp/source/utf8/cpp17.h:56–61

    }

    inline std::string utf32to8(std::u32string_view s)
    {
        std::string result;
        utf32to8(s.begin(), s.end(), std::back_inserter(result));
        return result;
    }

    inline std::u32string utf8to32(std::string_view s)
    {