[ao][sparsity] Serialization support (#80890)
Implemented dumping and loading of state_dicts and __get_state__ and __set_state__ functions.
hook and layer are removed from the data_groups dictionary before serializing.
In the future, might have to treat functions differently before serializing. Currently, it is being
treated similar to other types while serializing.
Test Plan:
```python test/test_ao_sparsity.py TestActivationSparsifier```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80890
Approved by: https://github.com/z-a-f
