[X86] IsNOT - fold PCMPGT(C, X) -> PCMPGT(X,C-1)

To invert the result, we can profitably commute a PCMPGT node if the LHS was a constant (C > min_signed_value): https://alive2.llvm.org/ce/z/LxcPqm

Allows the constant to fold, and helps reduce register pressure

Fixes #67347