fx quant: more typehints, part 3 (#48794)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48794
Adds typehints to function I/O in `torch/quantization/quantize_fx.py`,
for readability.
Test Plan:
```
mypy torch/quantization/
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25307084
fbshipit-source-id: 67bdf95b78836dcabc7d829e1854ca5b8ceb8346
