Make gen_annotated_args support kwargs (#98396)
This PR is to address the issue seeing in PR #97417 where the newly added op requires `kwargs`, however, currently tools/autograd/gen_annotated_fn_args.py does not support `kwargs`, only `func_args` are generated for test_overrides.py.
The PR adds a new field "is_kwargs" to each argument indicating whether it's a `kwargs` or not. See example:
```
annotated_args = {
torch._C._VariableFunctions._cast_Byte: [{'is_kwarg_only': 'False', 'name': 'self', 'simple_type': 'Tensor'}],
...
```
The full comparison of the generated file `annotated_fn_args.py` can be found here:
- **Before**: [P681991116](https://www.internalfb.com/phabricator/paste/view/P681991116)
- **After**: [P681994218](https://www.internalfb.com/intern/paste/P681994218/)
Differential Revision: D44698310
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98396
Approved by: https://github.com/ezyang
