[fx] GraphModule.src -> GraphModule.code (#43655)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43655
Pure, unadulerated bikeshed. The good stuff.
This makes things more consistent with ScriptModule.
Test Plan: Imported from OSS
Reviewed By: ZolotukhinM
Differential Revision: D23401528
Pulled By: suo
fbshipit-source-id: 7dd8396365f118abcd045434acd9348545314f44
