Allow usage of all `typing` members in annotations

```py
def foo() -> Never: ... # allowed
b = Union[int, str] # not allowed
```
`basedtyping` as well.
Maybe `types` as well.

We could modify `sitecustomize.py` to actually load these for real. (`mypy install-site-types` maybe)

```py
b = Union[int, str] # allowed
```

Start by reading sitecustomize.py and the issue's reference to `mypy install-site-types`. Check how `typing` members are currently made available to annotations, then verify the `Union[int, str]` example and the existing `Never` example. Done means the requested `typing` members are accepted in assignments as well as annotations, with the scope of `basedtyping` and `types` resolved.

Written by the indexing model from the issue text.