[JIT] Fix annotation extraction for named tuple (#81506)
Followup similar to https://github.com/pytorch/pytorch/pull/81334
In Python-3.10 type annotations from base class are not inherited to the
child class which leads to the following error:
```
% python -c "import torch;torch.jit.script(torch.nn.utils.rnn.pack_padded_sequence)"
...
PackedSequence(Tensor data, Tensor batch_sizes, Tensor sorted_indices, Tensor unsorted_indices) -> ():
Expected a value of type 'Tensor (inferred)' for argument 'sorted_indices' but instead found type 'Optional[Tensor]'.
Inferred 'sorted_indices' to be of type 'Tensor' because it was not annotated with an explicit type.
:
File "/Users/nshulga/git/pytorch-worktree/torch/nn/utils/rnn.py", line 197
data, batch_sizes, sorted_indices, unsorted_indices = _packed_sequence_init_args(
data, batch_sizes, sorted_indices, unsorted_indices)
return PackedSequence(data, batch_sizes, sorted_indices, unsorted_indices)
~~~~~~~~~~~~~~ <--- HERE
```
Which stems from the fact that `torch.nn.utils.rnn.PackedSequence.__annotations__` returns empty list for python-3.10 as seen below:
```
% conda run -n py_39 python3 -c "import sys;import torch;print(torch.nn.utils.rnn.PackedSequence.__annotations__, sys.version_info[:2])"
{'data': <class 'torch.Tensor'>, 'batch_sizes': <class 'torch.Tensor'>, 'sorted_indices': typing.Optional[torch.Tensor], 'unsorted_indices': typing.Optional[torch.Tensor]} (3, 9)
% conda run -n py_310 python3 -c "import sys;import torch;print(torch.nn.utils.rnn.PackedSequence.__annotations__, sys.version_info[:2])"
{} (3, 10)
```
Fix by checking annotations of parent class if base one does not have any.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81506
Approved by: https://github.com/suo
