[TensorExpr] Add simplification of length 0 and 1 For loops to IR Simplifier (#36348)
Summary:
Simplifies loops which can be collapsed down into a single block or removed entirely. E.g.
```
For 0..1 {
Statements...
}
```
Is now just `Block({Statements...})`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36348
Differential Revision: D21057959
Pulled By: nickgg
fbshipit-source-id: 2f95a19a965c4a6e023680e2cea9ea846e82d62e
