ns for fx: skip shadowing for torch.cat, and also for nodes with only kwargs (#76561)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76561
User model had syntax like `torch.cat(tensors=[x])`. This PR fixes two errors
to unbreak this in NS shadow model:
1. skip nodes which only have kwargs (instead of throwing an exception)
2. explicitly skip shadowing of `torch.cat` (since it's not supported anyways)
Test Plan:
```
python test/test_quantization.py -k test_op_with_only_kwargs_skips_shadowing
python test/test_quantization.py -k test_op_mul_add_cat_skips_shadowing
```
Reviewed By: hx89
Differential Revision: D36017356
Pulled By: vkuzo
fbshipit-source-id: 0da4840a62c2dac183f8294c2cec4fce262474b3
(cherry picked from commit 88409c1576e7f690708957b2baa285fc7961e9d6)
