torch.ao migration: stubs.py phase 1 (#64861)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64861
1. move the file
```
hg mv caffe2/torch/quantization/stubs.py caffe2/torch/ao/quantization/
```
2. create a new file in the old location and copy the imports
3. fix all call sites inside `torch`
ghstack-source-id: 137885365
Test Plan: buck test mode/dev //caffe2/test:quantization
Reviewed By: jerryzh168
Differential Revision: D30879678
fbshipit-source-id: a2d24f25d01064212aca15e94e8c78240ba48953
