[llvm] [CodeGen] Refactor DeadMIElim isDead and GISel isTriviallyDead (PR #105956)

[Tobias Stadler via llvm-commits]

tobias-stadler wrote:

Conflicts are due to introduction of FAKE_USE. This adds another edgecase to isDead, which I am not sure should really be there considering the other properties the instruction is supposed to have. I have raised this here: https://github.com/llvm/llvm-project/pull/86149#issuecomment-2318815019

https://github.com/llvm/llvm-project/pull/105956