Fabulist compiler does not build with C++ 20

[Pheubel]

As discussed on the NovelRT discord, currently there is code that does not compile in C++ 20, this has to do with a behavior change in std::accumulate.

Fabulist/compiler/lib/compiler/save.cpp

Lines 71 to 98 in 4e97124

	nlohmann::json result = std::accumulate(
	values.begin(), values.end(),
	nlohmann::json{},
	[is_array](nlohmann::json& result,
	decltype(values)::const_reference value)
	{
	if (is_array)
	{
	result.push_back(value.second);
	}
	else
	{
	std::visit([&result, &value = value.second](auto&& arg) {
	using T = std::decay_t<decltype(arg)>;
	if constexpr (std::is_same_v<T, double>)
	{
	result[std::to_string(arg)] = value;
	}
	else if constexpr (std::is_same_v<T, std::string>)
	{
	result[arg] = value;
	}
	}, value.first);
	}
	return result;
	});

As mentioned in discord, passing in nlohmann::json result as a value instead of a reference in the lambda function seems like the best way forward, it builds on both C++ 17 and C++ 20.