[llvm] [LoopVectorize] Use CodeSize as the cost kind for minsize (PR #124119)

[Sam Tebbs via llvm-commits]

https://github.com/SamTebbs33 commented:

I don't see anything aarch64 or arm-specific about these changes. Can the tests be moved to the parent folder?

https://github.com/llvm/llvm-project/pull/124119