add support for optional int list with scalar fill (#43262)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43262
Test Plan: Imported from OSS
Reviewed By: ezyang
Differential Revision: D23212049
Pulled By: bhosmer
fbshipit-source-id: c7ceb2318645c07d36c3f932c981c9ee3c414f82
