[quant][refactor] factor out get_combined_dict function (#47781)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47781
Test Plan: Imported from OSS
Reviewed By: supriyar
Differential Revision: D24900303
fbshipit-source-id: 1a2cb0ec536384abcd140e0d073f0965ed2800cd
