[llvm] [SCEV] Introduce SCEVUse, use it instead of const SCEV * (NFCI) (WIP). (PR #91961)

[Florian Hahn via llvm-commits]

fhahn wrote:

@nikic I updated the current version to include a pointer to the canonical SCEV. WDYT would be the next steps to make progress with the patch and the follow-ups? How much compile-time would we be willing to spend on this?

https://github.com/llvm/llvm-project/pull/91961