get_origin

Get the unsubscripted version of a type.

This supports generic types, Callable, Tuple, Union, Literal, Final, ClassVar,
Annotated, and others. Return None for unsupported types.

Examples::

    >>> P = ParamSpec('P')
    >>> assert get_origin(Literal[42]) is Literal
    >>> assert get_origin(int) is None
    >>> assert get_origin(ClassVar[int]) is ClassVar
    >>> assert get_origin(Generic) is Generic
    >>> assert get_origin(Generic[T]) is Generic
    >>> assert get_origin(Union[T, int]) is Union
    >>> assert get_origin(List[Tuple[T, T]][int]) is list
    >>> assert get_origin(P.args) is P