[AST] Migrate away from PointerUnion::dyn_cast (NFC)#125379

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

kazutakahirata:cleanup_001_PointerUnion_clang_AST_ExprCXXkazutakahirata/llvm-project:cleanup_001_PointerUnion_clang_AST_ExprCXXCopy head branch name to clipboard