[InstCombine] Fold sub(Y,and(lshr(X,C),1)) --> add(ashr(shl(X,(BW-1)-C),BW-1),Y) (PR53610)

As noted on PR53610, we can fold a 'bit splat' negation of a shifted bitmask pattern into a pair of shifts.

https://alive2.llvm.org/ce/z/eGrsoN

Differential Revision: https://reviews.llvm.org/D119715