[DAGCombiner] Use getAnyExtOrTrunc instead of getSExtOrTrunc in the zext(setcc) combine.

We're ANDing with 1 right after which will cause the SIGN_EXTEND to
be combined to ANY_EXTEND later. Might as well just start with an
ANY_EXTEND.

While there replace create the AND using the getZeroExtendInReg
helper to remove the need to explicitly create the VecOnes constant.