[Dynamo] Support torch.Tensor.fn as TorchVariable, not UserDefinedObjectVariable, preventing graph break (#93243)
As found in #92709, thanks to @ngimel and @jansel, currently `torch.Tensor.fn` points to `UserDefinedObjectVariable` rather than `TorchVariable`. The root cause is due to https://github.com/pytorch/pytorch/pull/92709#pullrequestreview-1273357406. To prevent this, build `TorchVariable` of `torch.Tensor.fn` pointing to `torch.ops.aten.fn`.
This issue propagates to `torch.Tensor.fn` causing graph break with `nopython=True`.
```python
import torch
import torch._dynamo as dynamo
#op = torch.ops.aten.abs_ # no graph break
op = torch.Tensor.abs_ # graph break
args = torch.empty(10)
def foo(args):
return op(args)
opt_foo = dynamo.optimize("inductor", nopython=True)(foo)
y_ = opt_foo(args)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93243
Approved by: https://github.com/jansel
