[llvm] [Utils] Hoist ValueMapper out of per-instruction remap loops in CloneFunction (PR #216014)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

please write the description yourself (https://llvm.org/docs/AIToolPolicy.html#details). putting in the description the LLM prompt is not useful, and you should verify correctness yourself, it seems like you didn't review this change yourself based on the description

https://github.com/llvm/llvm-project/pull/216014