[msan] Precommit tests for Arm NEON vector shift (#101420)

MSan currently does not correctly instrument most (all?) Arm NEON vector
shift instructions. This patch shows the current state of
instrumentation.

A followup patch will apply handleVectorShiftIntrinsic to most of the
vector shift instructions and update this test accordingly.

Test forked from llvm/test/CodeGen/AArch64/arm64-vshift.ll.

Author: thurstond