Adds `fakeQuantizePerTensorAffineOp` to pytorch (#19387)
Summary:
Adding fakequant op so that we can use it in pytorch models, the exact implementation might change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19387
Differential Revision: D13739657
fbshipit-source-id: d5cb084e843d236bb1da9827ac1ba3900ed99786
