Simplify inequality comparisons against ramps and min/max expressions.

This PR contains some work done inside simplify for the specialize_branched_loops branch. I am splitting this off of the main PR for specialize_branched_loops so that it is easier to review.

There are 2 basic changes here. First, I added simplify rules for handling LT nodes with vector args. More recently, I added some simplify rules for handling LT nodes with min/max args. These simplify rules are very important for the specialize_branched_loops work.