dynamic equality constraint (#99993)
This diff adds support for dynamic equality constraints of the form `dynamic_dim(x, 0) == dynamic_dim(y, 1)`. The process of constraint discovery can already understand equality guards between dimensions and suggests such equality constraints, so this closes the loop on that. Correspondingly we now raise `ConstraintViolation` when we find that such a guard is added on a dynamic dimension and the user did not specify such a constraint. (NOTE: This is distinct from a dynamic dimension being guarded equal to a constant, which is already an error.)
Differential Revision: [D45279437](https://our.internmc.facebook.com/intern/diff/D45279437/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99993
Approved by: https://github.com/tugsbayasgalan
