[llvm] [mlir] Make MLIR Value more consistent in terms of `const` "correctness" (NFC) (PR #72765)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

> Let's document somewhere at the top that the use-list of a value is a part of the value state. It's a bit deeper in the implementation and folks may be misunderstanding that, hence the changes to use list-related methods.

Done

https://github.com/llvm/llvm-project/pull/72765