make default string arguments in schemas human readable (#27088)
Summary:
[jit] String default args get printed as ascii values https://github.com/pytorch/pytorch/issues/25804
https://github.com/pytorch/pytorch/issues/25804
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27088
Differential Revision: D17689732
Pulled By: Krovatkin
fbshipit-source-id: f385b2fe44c5a2387bfcb6484edf7faa92bc8edf
