Fix InputSize/OutputSize for ivalue based operators (#17579)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17579
These methods previously just returned 0 when it was not a legacy operator,
making it impossible to convert some operators.
Reviewed By: dzhulgakov
Differential Revision: D14253094
fbshipit-source-id: 72bfdcf6da291a4ab80d1e0ceb20984b86edc408
