[quant] Refactor qembeddingbag to remove duplicate code (#45881)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45881
Test Plan:
python test/test_quantization.py TestQuantizedEmbeddingBagOps
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D24127892
fbshipit-source-id: 344ee71d335b8c1d668c647db88775632e099dbd
