IsExact does not handle `readonly` modifier

[Yaojian]

IsExact returns true when the only difference between two interfaces is the readonly modifier.

    interface A {
      value: string;
    }

    interface B {
      readonly value: string;
    }

    assert<IsExact<A, B>>(false);     // fails the compiler because `IsExact` returns `true`

I consider it as a bug.

[papb]

Agreed. I have been using expect-type for this kind of thing, I believe it was inspired by this package, and has had a few bug fixes, and already covers correctly this case you reported.