Builtin function evaluation in the semantic analyzer

[Jacajack]

Feature description

Builtin function evaluation needs to be implemented. This is needed for code such as:

module X {}

impl X {
	const ubus<4> x = 0;
	const ubus<3> y = 0;

	auto z = match (join(x, y)) {
		join(4u4, 4u3) => 4u11,
		join(3u4, 3u3) => 3u11,
		join(2u4, 2u3) => 2u11,
		join(1u4, 1u3) => 1u11,
		default => 0,
	};
}

Was experimenting with join-based-poor-man's-tuples.