[TensorExpr] Don't rely on exceptions in Vectorizer. (#64609)

[TensorExpr] Don't rely on exceptions in Vectorizer. (#64609)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64609

We've been using exceptions to indicate whether vectorization succeeded
or not, but that posed some problems with (e.g. we spent too much time
symbolicazing these exceptions). This change converts this mechanism to
a standard error return code.

Test Plan: Imported from OSS

Reviewed By: bertmaher

Differential Revision: D30795342

Pulled By: ZolotukhinM

fbshipit-source-id: 16e38b37bcdd78ceb438ac814cc377f35b058e17