ensure tooltips are closed when its parent detaches from visual tree.

src/Avalonia.Controls/ToolTipService.cs

@@ -28,14 +28,22 @@ namespace Avalonia.Controls
             {
                 control.PointerEnter -= ControlPointerEnter;
                 control.PointerLeave -= ControlPointerLeave;
+                control.DetachedFromVisualTree -= ControlDetaching;
             }
 
             if (e.NewValue != null)
             {
                 control.PointerEnter += ControlPointerEnter;
                 control.PointerLeave += ControlPointerLeave;
+                control.DetachedFromVisualTree += ControlDetaching;
             }
         }
+        
+        private void ControlDetaching(object sender, VisualTreeAttachmentEventArgs e)
+        {
+            var control = (Control)sender;
+            Close(control);
+        }
 
         /// <summary>
         /// Called when the pointer enters a control with an attached tooltip.