[TensorExpr] some cleanups / fixes for LoopOptions (#39408)
Summary:
Mainly, fix a bug in the HashProvider where it would not include LoopOptions in the hash, meaning two loops would be seen as identical even if they were bound to different thread/block axes. Also added symbolic names for the different axis options.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39408
Differential Revision: D21864494
Pulled By: nickgg
fbshipit-source-id: 9c28729984e7a3375e026c78294c9f75b9015123
