[quant][graphmode][fx] Add reference quantized linear module (#63627)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63627
Added reference quantized linear module for the custom backend flow, the reference quantized module will
have the following code:
```
w(float) -- quant - dequant \
x(float) ------------- F.linear ---
```
In the full model, we will see
```
w(float) -- quant - *dequant \
x -- quant --- *dequant -- *F.linear --- *quant - dequant
```
and the backend should be able to fuse the ops with `*` into a quantized linear
Test Plan:
python test/test_quantization.py TestQuantizeFx.test_conv_linear_reference
Imported from OSS
Reviewed By: vkuzo
Differential Revision: D30504750
fbshipit-source-id: 5729921745c2b6a0fb344efc3689f3b170e89500
