[bc-breaking][quant][be] Refactor fuser_method to include `is_qat` argument (#70009)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70009
Currently we rely on module.training to decide whether we'll do a qat fusion or ptq fusion, this is
not ideal since training flag has nothing to do with quantization, this PR introduces an extra flag `is_qat`
to control this
Note: currently we still has the constraint that when `is_qat` is True, the modules must be in training mode, we
can relax this constraint later
Test Plan:
```
python test/test_quantization.py TestFuseFx
python test/test_quantization.py TestFusion
```
Imported from OSS
**Static Docs Preview: classyvision**
|[Full Site](https://our.intern.facebook.com/intern/staticdocs/eph/D33178977/V36/classyvision/)|
|**Modified Pages**|
Reviewed By: mruberry
Differential Revision: D33178977
fbshipit-source-id: 0c1499c45526971140d9ad58e2994d1edf5ad770
(cherry picked from commit 2d51f9fb28967f1c5aab260d84b8d32d838f4f26)
