[llvm] [DAG] Add freeze(assertext(x)) -> assertext(x) folds (PR #94491)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Could you move the special handling of `assertext(x)` into `DAG.isGuaranteedNotToBeUndefOrPoison`? Then the combine above would handle your case transparently and we can use `isGuaranteedNotToBeUndefOrPoison`in other places.

https://github.com/llvm/llvm-project/pull/94491