Add deepcopy functionality to parametrized modules (#80811)
Fixes #69413
After applying parametrization to any `nn.Module` we lose the ability to create a deepcopy of it e.g. it makes it impossible to wrap a module by an `AveragedModel`.
Specifically, the problem is that the `deepcopy` tries to invoke `__getstate__` if object hasn't implemented its own `__deepcopy__` magic method. But we don't allow serialization of the parametrized modules: `__getstate__` raises an error.
My solution is just to create a default `__deepcopy__` method when it doesn't exist yet.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80811
Approved by: https://github.com/pearu, https://github.com/albanD
