[fx] add test for args/kwargs handling (#43640)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43640
+ added a `self.checkGraphModule` utility function to wrap the common
test assert pattern.
Test Plan: Imported from OSS
Reviewed By: gmagogsfm
Differential Revision: D23356262
Pulled By: suo
fbshipit-source-id: a50626dcb01246d0dbd442204a8db5958cae23ab
