ns for fx: move op dtype category mapping to separate file (#55858)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55858
Moves the mappings of input and output dtypes of various ops
into its own file, and makes the variable names more clear. No logic
change.
Test Plan:
```
python test/test_quantization.py TestFXNumericSuiteCoreAPIs
```
Imported from OSS
Reviewed By: raghuramank100
Differential Revision: D27740662
fbshipit-source-id: d384e7e542d9cc868d9cee9c53c2ac2f74a15a48
