TypedDict.keys() and items() should return KeysView and ItemsView

[crusaderky]

Reopened from python/mypy#7845 as requested

mypy incorrectly believes that TypedDict.keys() and TypedDict.items() return an AbstractSet, whereas it should be more accurately a KeysView and a ItemsView respectively:

from typing_extensions import TypedDict

class D(TypedDict):
    x: int

d: D
reveal_type(d.keys())
reveal_type(d.items())
reveal_type(d.values())

Output:

7: note: Revealed type is 'typing.AbstractSet[builtins.str*]'
8: note: Revealed type is 'typing.AbstractSet[Tuple[builtins.str*, builtins.object*]]'
9: note: Revealed type is 'typing.ValuesView[builtins.object*]'

Expected output:

7: note: Revealed type is 'typing.KeysView[builtins.str*]'
8: note: Revealed type is 'typing.ItemsView[builtins.str*, builtins.object*]'
9: note: Revealed type is 'typing.ValuesView[builtins.object*]'

[JukkaL]

This can actually be implemented by modifying the typeshed stub for typing (look for _TypedDict). Feel free to send a typeshed PR or create a typeshed issue.

[ilevkivskyi]

@JukkaL GitHub now supports direct transfer of issues between repos, I think it makes sense to just move it to typeshed.