[msan][NFCI] Add tests for Arm NEON vector load (#125267)

Forked from llvm/test/CodeGen/AArch64/arm64-ld1.ll

Incorrectly handled by handleUnknownInstruction:
- llvm.aarch64.neon.ld1x2, llvm.aarch64.neon.ld1x3,
llvm.aarch64.neon.ld1x4
- llvm.aarch64.neon.ld2, llvm.aarch64.neon.ld3, llvm.aarch64.neon.ld4
- llvm.aarch64.neon.ld2lane, llvm.aarch64.neon.ld3lane,
llvm.aarch64.neon.ld4lane
- llvm.aarch64.neon.ld2r, llvm.aarch64.neon.ld3r, llvm.aarch64.neon.ld4r

Author: thurstond