fx quant: move output obs logic to QuantizeHandler (#57377)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57377
Moves the logic which determines
1. whether a pattern instance's output should be observed
2. whether a pattern instance's output should be marked as observed based on its inputs
3. whether to ovverride the activation specified in the qconfig
from `quantize.py` to `quantization_patterns.py`. This makes
the code easier to read and reduces the coupling between `Quantizer`
and `QuantizeHandler` instances.
Note: there are some further cleanups which would be good after this one
- leaving those for future PRs.
Test Plan:
```
python test/test_quantization.py TestQuantizeFxOps
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D28126896
fbshipit-source-id: 94c80a9c7307452783348d65b402acc84983e3f6
