Extending Learnable Fake Quantize module to support gradient scaling and factory (partial) construction (#41969)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41969
In this diff, the `_LearnableFakeQuantize` module is extended to provide support for gradient scaling where the gradients for both scale and zero point are multiplied by a constant `g` (in some cases, can help with quicker convergence). In addition, it is also augmented to provide a factory method via `_with_args` such that a partial constructor of the module can be built.
Test Plan:
For correctness of the fake quantizer operators, on a devvm, enter the following command:
```
buck test //caffe2/torch:quantization -- learnable_py_module
```
Reviewed By: z-a-f
Differential Revision: D22715629
fbshipit-source-id: ff8e5764f81ca7264bf9333789f57e0b0cec7a72
