[dynamo][numpy] Add support for builtin len() on numpy ndarray (#105691)
Issue #105054
```
def fn(x):
v = x.sum() / len(x)
return v
```
This creates a graph break because we don't know how to handle __len__ method.
Solution is just delegate it back to `TensorVariable`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105691
Approved by: https://github.com/ezyang
