[ImageResizer] Fix issues with blank Width and Height controls (#37373)

* Allow custom preset's dimensions to be blank in the UI while still persisted as 0.

* XAML formatting - reorder namespaces.

* Add "(auto)" text to zero-value Width/Height in Settings. Ensure Width and Height fields in flyout are formatted to empty when their value is 0.

src/settings-ui/Settings.UI/SettingsXAML/Controls/ImageResizerDimensionsNumberBox.cs

@@ -0,0 +1,38 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Microsoft.PowerToys.Settings.UI.Controls;
+
+public partial class ImageResizerDimensionsNumberBox : NumberBox
+{
+    public ImageResizerDimensionsNumberBox()
+    {
+        this.Loaded += (_, _) => UpdateDisplayText();
+
+        this.ValueChanged += (_, _) => UpdateDisplayText();
+
+        this.GotFocus += (s, e) =>
+        {
+            // Show "0" in the UI when focused on the empty value. This ensures that the spinbutton
+            // controls are usable.
+            if (Value is double.NaN)
+            {
+                Value = 0.0;
+            }
+        };
+
+        this.LostFocus += (_, _) => UpdateDisplayText();
+    }
+
+    private void UpdateDisplayText()
+    {
+        if (FocusState == FocusState.Unfocused && Value == 0)
+        {
+            Text = string.Empty;
+        }
+    }
+}