popUntil method
Pop until id is top (removes layers above it).
Implementation
void popUntil(String id) {
final i = _indexOf(id);
if (i < 0) return;
while (_stack.length > i + 1) {
final removed = _stack.removeLast();
removed.reset();
removed.attachSend(null);
}
_notifyStack();
onPendingChanged?.call();
}