[Quant] Implemented 4 bit embedding op support; added corresponding test case (#69768)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69768
Support for the 4 embedding operator has been added. The support is analogous to the preexisting support for byte/8bit embedding. A corresponding test case was added to test_quantized_embedding_op.py
Test Plan:
In pytorch main dir, execute
```
python test/test_quantization.py TestStaticQuantizedModule.test_embedding_api
```
to run the series of tests, including the newly added test_embedding_4bit
function
Imported from OSS
Reviewed By: jbschlosser
Differential Revision: D33152673
fbshipit-source-id: bdcc2eb2e37de38fda3461ff3ebf1d2fb5e58071
