new refine entry for the atan2 function

- This resolves #8272
- This is linked with the previous PR #8273
I am not sure I understand your suggestion. The first 'if' or the third will catch , if I don't miss something,  already any combination that result in a negative ratio. the first one will catch negative/positive and the third will get positive/negative
```python
    if ask(Q.real(y) & Q.positive(x), assumptions):
        return atan(y / x)
    elif ask(Q.negative(y) & Q.negative(x), assumptions):
        return atan(y / x) - S.Pi
    elif ask(Q.positive(y) & Q.negative(x), assumptions):
        return atan(y / x) + S.Pi
```