fx quant: clarify state in Quantizer object (#43927)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43927
Adds uninitialized placeholders for various state
used throughout the Quantizer object, with documentation
on what they are. No logic change.
Test Plan:
```
python test/test_quantization.py TestQuantizeFxOps
python test/test_quantization.py TestQuantizeFx
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D23439473
fbshipit-source-id: d4ae83331cf20d81a7f974f88664ccddca063ffc
