[quant] AO migration of the `quantize.py` (resubmission) (#64445)

[quant] AO migration of the `quantize.py` (resubmission) (#64445)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64445

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/dev //caffe2/test:quantization`

Reviewed By: HDCharles

Differential Revision: D30734870

fbshipit-source-id: dc204f3cc46bff2cc81c95159eab9d333b43bb4b