Expose nbins and ratio (#50398)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50398
Test Plan: fbcode/caffe2/test/quantization/test_quantized_op.py
Differential Revision: D25873541
fbshipit-source-id: 7c3cdbb38a1e943e7fa8943a4195dc65d9d95105
