add Dimname support to IValue (#42054)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/42054
Test Plan: Imported from OSS
Reviewed By: smessmer
Differential Revision: D22750398
Pulled By: bhosmer
fbshipit-source-id: 7028268093f86b33c4117868b0edcb9e1ca6f7ee
