[TensorExpr] Move inner loops vectorization logic to its own method (#45287)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45287
Test Plan: CI, build
Reviewed By: gmagogsfm
Differential Revision: D23913432
Pulled By: asuhan
fbshipit-source-id: 3bf8fe09753f349e3c857863a43d2b1fca5101c1
