Migrate CPU tril, triu, masked_fill to c10::complex (#37897)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/37897
Test Plan: Imported from OSS
Differential Revision: D21442181
Pulled By: anjali411
fbshipit-source-id: 609af9086da1b622db51694f65eadfebe3970cfd
