Quantized vec256 + vectorized quantized::add
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/25202
Test Plan: Imported from OSS
Differential Revision: D17061047
Pulled By: jamesr66a
fbshipit-source-id: b08a61a9b4a258a4c1b6a97a6da1db05c3a6b0f7
