Adding dequantize_val and requantize_val
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/23909
Test Plan: Imported from OSS
Differential Revision: D16678276
Pulled By: zafartahirov
fbshipit-source-id: db0f3033774b44d6aed6e60e84b20b6f4c220ec0
