[wip] fast typeMeta/ScalarType conversion approach 2 (#44965)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/44965
Test Plan: Imported from OSS
Reviewed By: ezyang
Differential Revision: D23789657
Pulled By: bhosmer
fbshipit-source-id: 5afdd52d24bd097891ff4a7313033f7bd400165e
