Tuple-like typing for lists in type hints

[TruncatedDinoSour]

Hello python devs,

I always run into an issue like this while
working with Union data, so like I know
what elements will be in a list, but I don't
think there's a way to type them, so I always
have to use # type: ignore in certain places

Even though that description it's kinda meh,
here's what I mean:

x: Dict[str, List[int, int]]  # This is a `dict` of `list` which always
                              # has 2 elements -- int and int

For example

x: Dict[str, List[int, int]] = {
    "hi": [1, 2],
    "bye": [3, 1],
    "aaa": [79, 27],
    "haxxor": [1337, 420],
}

And things like this should fail:

x: Dict[str, List[int, int]] = {
    "hi": [1, 2],
    "bye": [3, 1],
    "aaa": [79, 27],
    "haxxor": [1337, 420, 69],  # error: Incompatible types in assignment (expression has type "List[int, int, int]", variable has type "List[int, int]")
}

Unions aren't as convenient...

[hauntsaninja]

Duplicate of #592