Add Viewbox to VisualTreeExtensions FindChild branches

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI/Extensions/FrameworkElement/FrameworkElementExtensions.LogicalTree.cs

@@ -196,6 +196,20 @@ public static partial class FrameworkElementExtensions
                     goto Start;
                 }
             }
+            else if (element is Viewbox viewbox)
+            {
+                if (viewbox.Child is FrameworkElement child)
+                {
+                    if (child is T result && predicate.Match(result))
+                    {
+                        return result;
+                    }
+
+                    element = child;
+
+                    goto Start;
+                }
+            }            
             else if (element is UserControl userControl)
             {
                 // We put UserControl right before the slower reflection fallback path as
@@ -398,6 +412,17 @@ public static IEnumerable<FrameworkElement> FindChildren(this FrameworkElement e
                     goto Start;
                 }
             }
+            else if (element is Viewbox viewbox)
+            {
+                if (viewbox.Child is FrameworkElement child)
+                {
+                    yield return child;
+
+                    element = child;
+
+                    goto Start;
+                }
+            }
             else if (element is UserControl userControl)
             {
                 if (userControl.Content is FrameworkElement content)