Support for MapValues

[haejunejung]

It provides support for MapValues. It is related to #44.

The MapValues type is useful when you need to work with just the values of a Map, allowing you to extract and use the value type.

type T0 = Map<string, string>;
type Expected = MapValues<T0> // string

type T1 = Map<string, '0' | '1' | '2'>;
type Expected = MapValues<T1> // '0' | '1' | '2'

Here's a detailed implementation. playground