TypedDict 'in' narrowing w/o @final

We shouldn't require @final decoration for TypedDicts to narrow them based on the 'in' operator.

Why?

Basically @erictraut's comment.

In #13838, we've added "key in Union[TypedDict, ...]" narrowing for TypedDicts that are marked @final. The reason was to prevent this:

class Mammal(TypedDict):
  mammary_glands: int

class Bird(TypedDict):
  eggs: int

class Echidna(Mammal):
  eggs: int

animal: Mammal | Bird
if 'eggs' in animal:
  assert_type(animal, Bird)  # WRONG! Could still be a Mammal (a Echidna)
if 'eggs' in animal and 'mammary_glands' in animal:
  assert_never(animal)  # WRONG! Could still be a Mammal (a Echidna)

However, per @erictraut's comment, due to TypedDict being a structural type, we shouldn't consider the class hierarchy when type-matching.

This will be consistent with pyright and TypeScript (Playground Link).

La issue non nomina file né test; inizia esaminando il narrowing esistente di key in Union[TypedDict, ...] aggiunto in #13838 e riproduci gli esempi precedenti. Considera completato il lavoro quando il narrowing è consentito senza @final, trattando i TypedDict in modo strutturale; aggiungi quindi la copertura di regressione per i casi mostrati e verifica che le asserzioni errate vengano rifiutate.