[DAG] Fold freeze(bitcast(x)) -> bitcast(freeze(x))

This is a very specific fold to fix an upstream poor codegen issue.

InstCombine has the much more flexible pushFreezeToPreventPoisonFromPropagating but I don't think we're quite there with DAG/TLI handling for canCreateUndefOrPoison/isGuaranteedNotToBeUndefOrPoison value tracking yet.

Fixes #54911

Differential Revision: https://reviews.llvm.org/D124185