[InstCombine] add `getFreeInverted` to perform folds for free inversion of op

With the current logic of `if(isFreeToInvert(Op)) return Not(Op)` its
fairly easy to either 1) cause regressions or 2) infinite loops
if the folds we have for `Not(Op)` ever de-sync with the cases we
know are freely invertible.

This patch adds `getFreeInverted` which is able to build the free
inverted op along with check for free inversion to alleviate this
problem.