Fix: Interactive element is no longer interactive after adding it a second time (#1550)

<!--- Provide a general summary of your changes in the Title above -->

## Description
- `AppTitleBarTextBox` 's `Width` is not set, so `Width +=1 ` does
nothing
- The `SizeChanged` event handler is called **once**, because of
`Visibility` changed, and it was put in a `StackPanel` that's vertically
constrained, so the size change will occur once, not because `Width +=
1`. Consecutive adding it to the title bar no longer triggers the event
handler, therefore the issue
- And `Width += 1` is a dirty hack anyway, does not need that.

## Motivation and Context
Close #1470

## How Has This Been Tested?
Manual.

## Types of changes
<!--- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

Author: HO-COOH

WinUIGallery/ControlPages/TitleBarPage.xaml.cs

@@ -192,6 +192,23 @@ private void defaultTitleBar_Click(object sender, RoutedEventArgs e)
             UIHelper.AnnounceActionForAccessibility(sender as UIElement, "TitleBar size and width changed", "TitleBarChangedNotificationActivityId");
         }
 
+        private void setTxtBoxAsPasthrough(FrameworkElement txtBoxNonClientArea)
+        {
+            GeneralTransform transformTxtBox = txtBoxNonClientArea.TransformToVisual(null);
+            Rect bounds = transformTxtBox.TransformBounds(new Rect(0, 0, txtBoxNonClientArea.ActualWidth, txtBoxNonClientArea.ActualHeight));
+
+            var scale = WindowHelper.GetRasterizationScaleForElement(this);
+
+            var transparentRect = new Windows.Graphics.RectInt32(
+                _X: (int)Math.Round(bounds.X * scale),
+                _Y: (int)Math.Round(bounds.Y * scale),
+                _Width: (int)Math.Round(bounds.Width * scale),
+                _Height: (int)Math.Round(bounds.Height * scale)
+            );
+            var rectArr = new Windows.Graphics.RectInt32[] { transparentRect };
+            SetClickThruRegions(rectArr);
+        }
+
         private void AddInteractiveElements_Click(object sender, RoutedEventArgs e)
         {
             var txtBoxNonClientArea = UIHelper.FindElementByName(sender as UIElement, "AppTitleBarTextBox") as FrameworkElement;
@@ -204,34 +221,26 @@ private void AddInteractiveElements_Click(object sender, RoutedEventArgs e)
             {
                 addInteractiveElements.Content = "Remove interactive control from titlebar";
                 txtBoxNonClientArea.Visibility = Visibility.Visible;
-                if (!sizeChangedEventHandlerAdded)
+                if (sizeChangedEventHandlerAdded)
+                {
+                    setTxtBoxAsPasthrough(txtBoxNonClientArea);
+                }
+                else
                 {
                     sizeChangedEventHandlerAdded = true;
                     // run this code when textbox has been made visible and its actual width and height has been calculated
                     txtBoxNonClientArea.SizeChanged += (object sender, SizeChangedEventArgs e) =>
                     {
                         if (txtBoxNonClientArea.Visibility != Visibility.Collapsed)
                         {
-                            GeneralTransform transformTxtBox = txtBoxNonClientArea.TransformToVisual(null);
-                            Rect bounds = transformTxtBox.TransformBounds(new Rect(0, 0, txtBoxNonClientArea.ActualWidth, txtBoxNonClientArea.ActualHeight));
-
-                            var scale = WindowHelper.GetRasterizationScaleForElement(this);
-
-                            var transparentRect = new Windows.Graphics.RectInt32(
-                                _X: (int)Math.Round(bounds.X * scale),
-                                _Y: (int)Math.Round(bounds.Y * scale),
-                                _Width: (int)Math.Round(bounds.Width * scale),
-                                _Height: (int)Math.Round(bounds.Height * scale)
-                            );
-                            var rectArr = new Windows.Graphics.RectInt32[] { transparentRect };
-                            SetClickThruRegions(rectArr);
+                            setTxtBoxAsPasthrough(txtBoxNonClientArea);
                         }
                     };
                 }
-                txtBoxNonClientArea.Width += 1; //to trigger size changed event
+
+                // announce visual change to automation
+                UIHelper.AnnounceActionForAccessibility(sender as UIElement, "TitleBar size and width changed", "TitleBarChangedNotificationActivityId");
             }
-            // announce visual change to automation
-            UIHelper.AnnounceActionForAccessibility(sender as UIElement, "TitleBar size and width changed", "TitleBarChangedNotificationActivityId");
         }
 
     }

WinUIGallery/Navigation/NavigationRootPage.xaml

@@ -59,8 +59,8 @@
             AutomationProperties.AutomationId="AppTitleBar"
             Canvas.ZIndex="1"
             IsHitTestVisible="True">
-            <StackPanel VerticalAlignment="Center" Orientation="Horizontal">
-                <Image Width="18" Source="ms-appx:///Assets/Tiles/TitlebarLogo.png" />
+            <StackPanel VerticalAlignment="Stretch" Orientation="Horizontal">
+                <Image Width="18" VerticalAlignment="Center" Source="ms-appx:///Assets/Tiles/TitlebarLogo.png" />
                 <TextBlock
                     x:Name="AppTitle"
                     Margin="12,0,0,0"