add quantized version of hardswish operator (#34820)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34820
Adds quantized version of hardswish, for common quantized operator coverage.
Note:
* we carry over scale and zero_point from the input to the output, because the
range of the output is unbounded if x > 0
* we also skip the .out function to not allow the user to specify a custom
scale+zp (flexible on this).
Test Plan:
```
python test/test_quantized.py
https://gist.github.com/vkuzo/f9b579315ed7f5fdb24839e3218d8465
```
Imported from OSS
Differential Revision: D20472905
fbshipit-source-id: 0f2a83e9f5f7b43485fa46caf30e756dc5d492a9
