Update arrangement logic for containers, remove position property from Rect, add Size property to IElement.

Voile/Source/UI/Widgets/Widget.cs

@@ -7,11 +7,12 @@ namespace Voile.UI.Widgets;
 /// <summary>
 /// A base class for all UI widgets.
 /// </summary>
-public abstract class Widget : IElement, IRenderableElement, IInputElement
+public abstract class Widget : IElement, IRenderableElement, IInputElement, IResizeableElement, IUpdatableElement
 {
     public bool Visible { get; set; } = true;
     public bool IgnoreInput { get; set; }
     public Vector2 Position { get; set; } = Vector2.Zero;
+    public Rect Size { get; set; } = new();
 
     public Widget()
     {
@@ -23,9 +24,7 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement
         Position = position;
     }
 
-    /// <summary>
-    /// Get a minimum rectangle size for this widget.
-    /// </summary>
+    /// </inheritdoc>
     public abstract Rect MinimumRect { get; }
 
     /// <summary>
@@ -38,4 +37,12 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement
     /// </summary>
     /// <param name="action">An input action this widget received.</param>
     public abstract void Input(IInputAction action);
+
+    public void Update()
+    {
+        if (Size == Rect.Zero)
+        {
+            Size = MinimumRect;
+        }
+    }
 }