[quant] Add a quantized batch_norm operator (#33080)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33080
Quantized batch norm for cases where batch norm cannot be fused with conv.
AVX2 implementation is from Caffe2.
Test Plan:
python test/test_quantized.py TestQuantizedOps.test_batch_norm
Imported from OSS
Differential Revision: D19861927
fbshipit-source-id: bd8cd101fc063cb6358132ab7c651a160999293c
