Support for TupleToUnion

[haejunejung]

It provides support for TupleToUnion.

There are some situations that need to change tuple to union type.
It is more detailed example for API Response that is used TupleToUnion.

type ApiResponse = [number, string, boolean, { key: string }];
type AllowedValues = TupleToUnion<ApiResponse>; // number | string | boolean | { key: string }

function handler (response: AllowedValues) {
 if (typeof response === 'number') { // }
 else if (typeof response === 'string) { // }
 else if (typeof response === 'boolean) { // }
 else { // }
}