Function insert_iterator

Source/external/json.hpp:22436–22451

	///		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/