[DAG] Move "xor (X logical_shift ShiftC), XorC --> (not X) logical_shift...

[DAG] Move "xor (X logical_shift ShiftC), XorC --> (not X) logical_shift ShiftC" fold into SimplifyDemandedBits

SimplifyDemandedBits is called slightly later which allows the not(sext(x)) -> sext(not(x)) fold to occur via foldLogicOfShifts

As mentioned on D127115, we should be able to further generalise this based off the demanded bits.