fx quant: more typehints, part 2 (#48792)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48792
Adds some more typehints throughout quantization/fx/quantize.py,
to help with readability.
Test Plan:
```
mypy torch/quantization/fx/quantize.py
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25306683
fbshipit-source-id: fc38b885a2cb5bf2c6d23b6305658704c6eb7811
