Unify Quantization APIs for add, pool and relu (#26335)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26335
Use the backend engine flag to call QNNPACK for quantized ops.
Test Plan:
python test/test_quantized.py TestQNNPACKOps
Imported from OSS
Differential Revision: D17504331
fbshipit-source-id: 35cb2189067ac5cc6a7307179ef0335d1cec7b8f
