Rename qint8 data type (#19932)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19932
In preparation to add int8_t data type for QTensor
Reviewed By: zafartahirov
Differential Revision: D15137838
fbshipit-source-id: 59462c36d6fc5982986d4196bf3f32f49bb294d7
