different bounds for same Dim name (#110638)
Previously,`Dim` definitions that shared the same name but had different ranges were allowed to appear in the `dynamic_shapes` argument of an `export` call. They would correspond to the *same* dynamic dimension (identified by the shared name) with an effective range would be the *intersection* of the different ranges.
However this behavior can be confusing, because having different definitions with the same name is more likely than not unintentional. Therefore, this PR makes it a user error.
We still allow different definitions with the same name to exist at the same time (no global uniqueness) as long as they are not confused in the same `export` call. Redefinitions with the same bounds are also allowed, in case they are accidentally created by executing the same code multiple times.
Differential Revision: [D49965944](https://our.internmc.facebook.com/intern/diff/D49965944/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110638
Approved by: https://github.com/zhxchen17
