feat: implement layer change.

src/Ursa/Controls/Dialog/DialogLayerChangeEventArgs.cs

@@ -0,0 +1,18 @@
+namespace Ursa.Controls;
+
+public class DialogLayerChangeEventArgs
+{
+    public DialogLayerChangeType ChangeType { get; }
+    public DialogLayerChangeEventArgs(DialogLayerChangeType type)
+    {
+        ChangeType = type;
+    }
+}
+
+public enum DialogLayerChangeType
+{
+    BringForward,
+    SendBackward,
+    BringToFront,
+    SendToBack
+}