Introduce constrain_range; remove old expr_subs (#95063)
This PR introduces a new `constrain_range` function which can be used to constrain the possible values a SymInt/SymFloat can take on. This knowledge can be then used to discharge potential guards (by running the range analysis, and then seeing if the guard must be true given the original range) without adding another guard.
The usage of ranges is very limited right now; ranges are only constrained when the user explicitly instructs the system so. However, we can also infer range constraints based on guards as well; this is left for future work.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95063
Approved by: https://github.com/eellison
