case(Awaited): add nested thenable case - #38198

add Test Case to Awaited

The current cases cover nested Promises (Z, Z1) and a single-level thenable (T), but not a thenable whose resolved value is itself a thenable.

A solution that recurses only on Promise instead of PromiseLike passes all the existing cases but stops one level early on this one, while the built-in Awaited keeps unwrapping it down to number. Added T1 following the existing T case:

type T1 = { then: (onfulfilled: (arg: T) => any) => any }
// ...
Expect<Equal<MyAwaited<T1>, number>>,