Use `fbgemm` for quantize/dequantize ops (#19500)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19500
Changes the `quantize_linear` and `dequantize` to `fbgemm`-based implementation.
Reviewed By: jianyuh, jerryzh168
Differential Revision: D15014561
fbshipit-source-id: b651e69d336b5b08b4a75a4a4eddf46c040a4934
