[quant][qat] Ensure fake_quant and observer can be disabled on scriptmodule (#44773)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44773
The model is created and prepared using fx APIs and then scripted for training.
In order to test QAT on scriptmodel we need to be able to disable/enable fake_quant
and observer modules on it.
Test Plan:
python test/test_quantization.py TestQuantizeFx.test_qat_and_script
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D23741354
fbshipit-source-id: 3fee7aa9b049d9901313b977710f4dc1c4501532
