[quant] Support 4-bit embedding_bag operators using the dtype quint4x2 (#45752)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45752
Use the torch.quint4x2 dtype to create 4-bit packed tensors in the previous PR.
These packed tensors can be directly consumed by the operator.
Serialization of the packed tensors is supported using torchbind custom class.
Module support will follow in a later PR.
Test Plan:
python test/test_quantization.py TestEmbeddingBagOps
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D24120996
fbshipit-source-id: 2639353b3343ebc69e058b5ba237d3fc56728e1c
