A `Warn` intrinsic type

[kaleidawave]

There could be a new intrinsic type that allows the argument but raises an error when it is matched.

This would enable the technically correct, but unideal behaviour of functions like Math.sin

type NumberLike = number | Warn<any, "implicit cast">;
//                         ^^^^

interface Math {
	sin(x: NumberLike): number;
}

declare const Math: Math;

// Warning (not error): "2.2" is allowed but is a "implicit cast"
Math.sin("2.2") 

This is aimed at avoiding false positives in constraint inference #197 #35