toString_ method
Transform the value to a string.
Implementation
StringBuilder toString_({String? message}) {
// Use the toString() transformer from transformers.dart (imported unprefixed)
// but qualify via a helper variable to avoid confusion with Object.toString.
if (chain.coercedToString) return StringBuilder(chain: chain);
chain.setTransform(CoercionKind.string_, (child) => tr.toString(child));
return StringBuilder(chain: chain);
}