Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.UWP/Controls/WinoNavigationViewItem.cs

@@ -0,0 +1,47 @@
+using System.Numerics;
+using Microsoft.UI.Xaml.Controls;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Hosting;
+
+namespace Wino.Core.UWP.Controls
+{
+    public class WinoNavigationViewItem : NavigationViewItem
+    {
+        public bool IsDraggingItemOver
+        {
+            get { return (bool)GetValue(IsDraggingItemOverProperty); }
+            set { SetValue(IsDraggingItemOverProperty, value); }
+        }
+
+        public static readonly DependencyProperty IsDraggingItemOverProperty = DependencyProperty.Register(nameof(IsDraggingItemOver), typeof(bool), typeof(WinoNavigationViewItem), new PropertyMetadata(false, OnIsDraggingItemOverChanged));
+
+        private static void OnIsDraggingItemOverChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
+        {
+            if (obj is WinoNavigationViewItem control)
+                control.UpdateDragEnterState();
+        }
+
+        private void UpdateDragEnterState()
+        {
+            // TODO: Add animation. Maybe after overriding DragUI in shell?
+
+            //if (IsDraggingItemOver)
+            //{
+            //    ScaleAnimation(new System.Numerics.Vector3(1.2f, 1.2f, 1.2f));
+            //}
+            //else
+            //{
+            //    ScaleAnimation(new System.Numerics.Vector3(1f, 1f, 1f));
+            //}
+        }
+
+        private void ScaleAnimation(Vector3 vector)
+        {
+            if (Content is UIElement content)
+            {
+                var visual = ElementCompositionPreview.GetElementVisual(content);
+                visual.Scale = vector;
+            }
+        }
+    }
+}