update HistogramObserver to be scriptable (#51081)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51081
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51001
fix tests in TestQuantizeJitOps
Test Plan:
Imported from OSS
python test/test_quantization.py
Reviewed By: raghuramank100
Differential Revision: D26038759
Pulled By: lyoka
fbshipit-source-id: 0977ba7b8b26a9f654f20f5c698a7a20ec078c35
