ns for fx: initial support for int8 shadows fp32 (#60419)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60419
Adds support for NS for FX shadowed activations pass to handle int8
modules shadowing fp32 modules. The difficulty here is that in order
to insert the dtype cast, we need the qparams of the input.
For the current PR, we only handle the easy cases where the previous
node is either a `quantize_per_tensor` or an OSS quantized module.
A future PR can handle more complicated cases such as various functions.
Test Plan:
```
python test/test_quantization.py TestFXNumericSuiteCoreAPIs.test_int8_shadows_fp32_simple
```
Imported from OSS
Reviewed By: hx89
Differential Revision: D29280050
fbshipit-source-id: 465257c9f82a34fa91b48ae8887355c68e00edc6
