Fix bug replacing of root widget on UIKit

[Alex009]

Hello!

We find bug on iOS with UIKit and redwood. Case:
create uikit with root UIStackView - just like in CounterApp sample:

let container = UIStackView()
container.axis = .horizontal
container.alignment = .fill
container.distribution = .fillEqually
container.translatesAutoresizingMaskIntoConstraints = false

view.addSubview(container)
container.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
container.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
container.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
container.heightAnchor.constraint(equalTo: view.heightAnchor).isActive = true

self.delegate = CounterViewControllerDelegate(root: container)

in delegate use RedwoodUIView(root):

val composition = RedwoodComposition(
  scope = scope,
  view = RedwoodUIView(root),
  provider = SchemaWidgetFactories(
    Schema = IosWidgetFactory,
    RedwoodLayout = UIViewRedwoodLayoutWidgetFactory(),
  ),
)

but in Composable of our screen we should change root view by some condition (for example we change loading state to successful):

@Composable
fun Counter(value: Int = 0) {
  var count by rememberSaveable { mutableStateOf(value) }

  if (count == 3) {
    Text("this is end")
    return
  }
  
  Column(
    width = Constraint.Fill,
    height = Constraint.Fill,
    horizontalAlignment = CrossAxisAlignment.Center,
    verticalAlignment = MainAxisAlignment.Center,
  ) {
    Button("-1", onClick = { count-- })
    Text("Count: $count")
    Button("+1", onClick = { count++ })
  }
}

but istead of change root uiview we see that no changes.
reason - UIStackView add new child in arrangedSubviews (at 0 index) but remove child from subviews (that have different order). so when new UILabel added this label will be removed, instead of remove ColumnUIView

[JakeWharton]

Thanks! I'd like to get a test case in for this somewhere. Probably another subclass of the abstract children test.