Enable torch._refs.mean for nvFuser executor (#79444)
This PR fixes a bug with `broadcast_in_dim` leading to the situation when reduction ops were not allowed to be used before `broadcast_in_dim`.
With this PR it's possible to run
```py
import torch
import torch._refs
from torch._prims.executor import make_traced
def foo(a):
return torch._refs.mean(a, keepdim=False)
a = torch.randn(3, 3, device='cuda')
make_traced(foo)(a, executor="nvfuser")
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79444
Approved by: https://github.com/mruberry, https://github.com/jjsjann123
