[quant][graph] Add a new observer type for dynamic quantization (#35265)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35265
In graph mode we need to observer the activation tensor for dynamic quantization. This observer should behave the same way as the quantization functions called in the dynamic operator.
Currently for qlinear_dynamic we call quant_utils::ChooseQuantizationParams which has its own logic for calculating scale and zero_point.
We mimic those calculations in the new observer.
Test Plan:
python test/test_quantization.py ObserverTest
Imported from OSS
Differential Revision: D20630988
fbshipit-source-id: 7e7aca77590f965dcb423a705e68d030aaf98550
