Added late-canonicalize-term-changes
Added late-canonicalize-term-changes

Given an expression, and the location of that expression, returns the
changes required to "late-canonicalize" that expression, assuming it is
a proper term. This means that we sort the vars in a canonical ordering,
with all constants merged and moved to the front, for better cancellation.

jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie