Unions of TypedDicts don't work as expected

[JukkaL]

Operations on unions of typed dicts seem to use the fallback types, resulting in unexpected types:

from mypy_extensions import TypedDict
from typing import Union

class A(TypedDict):
    x: int
    y: str

class B(TypedDict):
    x: str

d: Union[A, B]
reveal_type(d['x'])  # builtins.object (expected: Union[int, str])
reveal_type(d.get('x'))  # builtins.object (expected: Union[int, str, None])

[grantwwu]

Here is an additional example, noting that you don't need conflicting types to hit this issue:

from mypy_extensions import TypedDict
from typing import Union


class A(TypedDict):
    x: int
    y: str


class B(TypedDict):
    x: int


d: Union[A, B]
reveal_type(d["x"]) # Revealed type is 'builtins.object*' (expected: int)