Preserve codegen on fx graph in transformer (#74189)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74189
Use the codegen on the original graph module for the new graph module produced by transformer.
Test Plan: Added a unit test: test_custom_codegen_with_transformer
Reviewed By: yinghai
Differential Revision: D34867938
fbshipit-source-id: fcda6600faeccfa7a650ba7226ca125e8440b19c
(cherry picked from commit d098c12081f61ddcf69052db5b8a1f31b0a0b67b)
