[DAG] Move vselect(icmp_ult, -1, add(x,y)) -> uaddsat(x,y) to DAGCombine (PR40111)

Move the X86 VSELECT->UADDSAT fold to DAGCombiner - there's nothing target specific about these folds.

The SSE42 test diffs are relatively benign - its avoiding an extra constant load in exchange for an extra xor operation - there are extra register moves, which is annoying as all those operations should commute them away.

Differential Revision: https://reviews.llvm.org/D91876