ns for fx: move shadow activations linear test to new API (#53819)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53819
Moves the linear tests for shadow activations to new API.
In order to do so, adds logic for fp32 to fp32 dtype cast,
which is an identity.
Test Plan:
```
python test/test_quantization.py TestFXNumericSuiteCoreAPIsModels.test_compare_shadow_activations_linear
```
Imported from OSS
Reviewed By: hx89
Differential Revision: D26982734
fbshipit-source-id: b6203228abf3cdf74ab0638468a6df77658aa662
