[Sema] Migrate away from PointerUnion::dyn_cast (NFC)#124675

kazutakahirata merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_001_PointerUnion_clang_Sema_TreeTransformkazutakahirata/llvm-project:cleanup_001_PointerUnion_clang_Sema_TreeTransformCopy head branch name to clipboard