Function insert_iterator

extern/json/json.hpp:22480–22495

    ///        see https://github.com/nlohmann/json/pull/1257
    template<typename... Args>
    iterator insert_iterator(const_iterator pos, Args&& ... args)
    {
        iterator result(this);
        JSON_ASSERT(m_value.array != nullptr);

        auto insert_pos = std::distance(m_value.array->begin(), pos.m_it.array_iterator);
        m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
        result.m_it.array_iterator = m_value.array->begin() + insert_pos;

        // This could have been written as:
        // result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
        // but the return value of insert is missing in GCC 4.8, so it is written this way instead.

        set_parents();
        return result;
    }

    /// @brief inserts element into array
    /// @sa https://json.nlohmann.me/api/basic_json/insert/