add hardsigmoid FP operator to PyTorch (#34545)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34545
This is for common operator coverage, since this is widely used. A future PR
will add the quantized version.
Some initial questions for reviewers, since it's my first FP operator
diff:
* do we need a backwards.out method for this?
* do we need CUDA? If yes, should it be this PR or is it ok to split
Test Plan:
```
// test
python test/test_torch.py TestTorchDeviceTypeCPU.test_hardsigmoid_cpu_float32
// benchmark
python -m pt.hardsigmoid_test
...
Forward Execution Time (us) : 40.315
Forward Execution Time (us) : 42.603
```
Imported from OSS
Differential Revision: D20371692
fbshipit-source-id: 95668400da9577fd1002ce3f76b9777c6f96c327
