[AST] Migrate away from PointerUnion::dyn_cast (NFC)#125157

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

kazutakahirata:cleanup_001_PointerUnion_clang_AST_ParentMapContextkazutakahirata/llvm-project:cleanup_001_PointerUnion_clang_AST_ParentMapContextCopy head branch name to clipboard