[pt2 export]fix name collision on constant name (#121145)
Summary: Taking the right most part of the fqn will cause name conflict when having multiple instances of the same class. Changed to replace "." in fqn by "_" to avoid invalid syntax in input args.
Test Plan: added test case
Differential Revision: D54435230
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121145
Approved by: https://github.com/zhxchen17
