[FX] Make TracerBase._find_user_frame private (#53654)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/53654
Test Plan: Imported from OSS
Reviewed By: suo, Chillee
Differential Revision: D26924950
Pulled By: jamesr66a
fbshipit-source-id: 23e641bbcabff148c18db0edeff0a12c10b8c42d
