[MLIR] Add a foldTrait() mechanism to allow traits to define folding and test...

[MLIR] Add a foldTrait() mechanism to allow traits to define folding and test it with an Involution trait

This change allows folds to be done on a newly introduced involution trait rather than having to manually rewrite this optimization for every instance of an involution

Reviewed By: rriddle, andyly, stephenneuendorffer

Differential Revision: https://reviews.llvm.org/D88809