dynamic range constraint API (#98779)
This diff adds the ability to specify range constraints on dynamic dimensions. (Previously we only supported declaring a dynamic dimension, which gets the default range `[2, sympy.oo]`.)
One point worth calling out: our initial design called for compound expressions like `lower <= dynamic_dim(x, d) <= upper`. However this seems difficult to support, because of a combination of desugaring and overloading semantics for such compound expressions in Python. Rather than silently doing the wrong thing, we explicitly error in this case and recommend users to specify multiple constraints, which is supported.
Differential Revision: [D44847318](https://our.internmc.facebook.com/intern/diff/D44847318/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98779
Approved by: https://github.com/ezyang
