fx quant: improve types on convert (#49688)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49688
Adds more types on FX quantize convert, fixing things as they
are uncovered by mypy.
Test Plan:
```
mypy torch/quantization
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25667231
fbshipit-source-id: 262713c6ccb050a05e3119c0457d0335dde82d25
