[Dynamo] torch.Generator state should have a source and be reconstructed properly (#97403)
Fixes #97077 partially.
During FX graph propagation, we request every tensor should have source:
https://github.com/pytorch/pytorch/blob/a524123c91ab399c9dd6882c1189596dd77e7734/torch/_dynamo/variables/builder.py#L929
However, the output of ```torch.Generator.get_state()``` is a tensor but without source, since it's generated inside of the FX graph. My change is following what we did for [Python random functions](https://github.com/pytorch/pytorch/blob/master/torch/_dynamo/variables/user_defined.py#L260), to have a dedicated ```GeneratorStateSource```. We have to also update the reconstruction logics, since we will reuse the ```TensorVariable``` reconstruction.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97403
Approved by: https://github.com/jansel, https://github.com/mlazos
