Union[A,B] type hint yields [user class A, user class B] instead of [instance A, instance B]

Subj.

```python
from typing import Union
class A:
  pass
class B:
  pass
def a() -> Union[A,B]: ...
def b() -> A: ...
```
Analysis of `a`'s return type gives back a set of user class A and user class B, whereas it should be instance A and instance B.
For comparison, analysis of `b`'s return type gives back a set of instance A.