[llvm] [Transforms] LoopIdiomRecognize recognize strlen and wcslen (PR #108985)

[Henry Jiang via llvm-commits]

mustartt wrote:

> If you seek another review, can you summerize the important changes? E.g. "[refactor with SCEV Expander](https://github.com/llvm/llvm-project/pull/108985/commits/86497d24934ad14a9bcb9ff16d079dd68c1c7890)" sounds significant. Any non-NFC changes?

It's a pure rebase since the last review. I finally had the chance to look at the CI problems. There were some failing LLDB test cases and a merge conflict. 

https://github.com/llvm/llvm-project/pull/108985