[quant] AO migration of the `quantize.py` (#64086)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64086
AO Team is migrating the existing torch.quantization into torch.ao.quantization. We are doing it one file at a time to make sure that the internal callsites are updated properly.
This migrates the `quantize.py` from torch.quantization to `torch.ao.quantization`.
At this point both locations will be supported. Eventually the torch.quantization will be deprecated.
Test Plan: `buck test mode/opt //caffe2/test:quantization`
Reviewed By: jerryzh168, raghuramank100
Differential Revision: D30055886
fbshipit-source-id: 8ef7470f9fa640c0042bef5bb843e7a05ecd0b9f
