Panels must be created before its descendents

[BadMagic100]

Describe the bug
If a Panel is created after any of its ancestors, the background of the panel will appear in front of (and likely obscure) those elements.

To Reproduce
Minimal repro:

LayoutRoot layout = new(true);
TextObject t = new(layout) { Text = "You can't see me", ContentColor = Colors.black };
Panel p = new(layout, BuiltInSprites.CreateBox()) { Child = t };

Expected behavior
Elements of a Panel should appear in front of the background regardless of creation order.

Additional context
This likely needs some flavor of explicit z-ordering.