fast-path is_complex() in the dispatcher (#50054)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50054
Test Plan: Imported from OSS
Reviewed By: swolchok
Differential Revision: D25760987
Pulled By: bdhirsh
fbshipit-source-id: 24666d3b86df6799ebbc478fdcdcaa445daff439
