[fix] complex type promotion (#77524)
Fixes https://github.com/pytorch/pytorch/issues/76803
Before Fix:
```python
>> a = torch.randn((2, 2), dtype=torch.float)
>> b = torch.tensor(1, dtype=torch.cdouble)
>> (a + b).dtype
torch.complex128
```
After Fix:
```python
>> a = torch.randn((2, 2), dtype=torch.float)
>> b = torch.tensor(1, dtype=torch.cdouble)
>> (a + b).dtype
torch.complex64
```
**Note**: This is a BC Breaking change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77524
Approved by: https://github.com/anjali411, https://github.com/mruberry
