[VP] Mark llvm.experimental.vp.splice as having no functional equivalent (#70647)

llvm.experimental.vp.splice has different semantics from
llvm.experimental.splice (since it takes uses the EVL arguments in a way
other
than just masking the tail elements), so it shouldn't be expanded to the
unpredicated version.

Coincidentally there's no support for llvm.experimental.vp.splice in
ExpandVectorPredication, so it wasn't getting expanded, but we shouldn't
mark
it as functionally equivalent anyway since there's other users of the
property
now e.g. in VectorCombine.

Author: lukel97

llvm/include/llvm/IR/VPIntrinsics.def

@@ -699,7 +699,7 @@ VP_PROPERTY_NO_FUNCTIONAL
 END_REGISTER_VP(vp_merge, VP_MERGE)
 
 BEGIN_REGISTER_VP(experimental_vp_splice, 3, 5, EXPERIMENTAL_VP_SPLICE, -1)
-VP_PROPERTY_FUNCTIONAL_INTRINSIC(experimental_vector_splice)
+VP_PROPERTY_NO_FUNCTIONAL
 END_REGISTER_VP(experimental_vp_splice, EXPERIMENTAL_VP_SPLICE)
 
 ///// } Shuffles