Add `weights_only` option to `torch.load` (#86812)
This addresses the security issue in default Python's `unpickler` that allows arbitrary code execution while unpickling.
Restrict classes allowed to be unpicked to in `None`, `int`, `bool`, `str`, `float`, `list`, `tuple`, `dict`/`OrderedDict` as well as `torch.Size`, `torch.nn.Param` as well as `torch.Tensor` and `torch.Storage` variants.
Defaults `weights_only` is set to `False`, but allows global override to safe only load via `TORCH_FORCE_WEIGHTS_ONLY_LOAD` environment variable.
To some extent, addresses https://github.com/pytorch/pytorch/issues/52596
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86812
Approved by: https://github.com/ezyang
