Fix quantized embedding export logic (#3095)

Summary:
Add patches to make 4bit quantized embedding work for export. Fixed:
* Schema mismatch between functional embedding_4bit and out variant
* Set `packed=True` for 4bit quantization

Pull Request resolved: https://github.com/pytorch/executorch/pull/3095

Reviewed By: mikekgfb

Differential Revision: D56340670

Pulled By: larryliu0820

fbshipit-source-id: c98623a9b7633fc5a6c390be1557213c719fa95a