[quant][graphmode][fx] Factor out run_weight_observer (#59029)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59029
Trying to remove Quantizer class and split prepare and convert code
Test Plan:
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
Imported from OSS
Reviewed By: vkuzo
Differential Revision: D28724864
fbshipit-source-id: 67ac5e7eb351970fdf46532c3c2ac6ac831bc697
