[quant] add serialization method for quantized hardswish (#94486)
**Summary**
Fix the issue: https://github.com/pytorch/pytorch/issues/91877. The root cause is serialization and deserialization method for `state_dict` does not enable for `QuantizedHardswish`. Added these methods in this PR.
**Test plan**
```
python -m pytest quantization/core/test_quantized_module.py -k test_hard_swish
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94486
Approved by: https://github.com/jgong5, https://github.com/vkuzo
