popTo method
Pop back to the level with id, if it exists in the stack.
Implementation
void popTo(String id) {
if (_disposed) return;
final idx = value.stack.indexWhere((l) => l.id == id);
if (idx < 0 || idx == value.stack.length - 1) return;
value = DrillDownState(stack: value.stack.sublist(0, idx + 1));
}