[DAGCombine] fold (urem x, (lshr pow2, y)) -> (and x, (add (lshr pow2, y), -1))

We have the same fold in InstCombine - though implemented via OrZero flag on isKnownToBePowerOfTwo. The reasoning here is that either a) the result of the lshr is a power-of-two, or b) we have a div-by-zero triggering UB which we can ignore.

Differential Revision: https://reviews.llvm.org/D129606