[msan][NFC] Add tests for Arm NEON smaxv/sminv (#129741)
This patch precommits tests for the smaxv/sminv intrinsics, which are
currently handled suboptimally by visitInstruction.
These are the signed versions of umaxv/uminv
(https://github.com/llvm/llvm-project/pull/129661).
Future work will update MSan to apply handleVectorReduceIntrinsic.
