Make sure ImageButton always has a background (dotnet#22717)

The OS does not specify a background so we need to make sure there is
a transparent background to get the ripple and border.

src/Core/src/Platform/Android/ButtonExtensions.cs

@@ -59,7 +59,9 @@ internal static void UpdateButtonStroke(this MaterialButton platformView, IButto
 
 		internal static void UpdateButtonBackground(this MaterialButton platformView, IButton button)
 		{
-			platformView.UpdateMauiRippleDrawableBackground(button,
+			platformView.UpdateMauiRippleDrawableBackground(
+				button.Background,
+				button,
 				() =>
 				{
 					// Copy the tints from a temporary button.

src/Core/src/Platform/Android/ImageButtonExtensions.cs

@@ -1,6 +1,7 @@
 using System.Threading.Tasks;
 using Google.Android.Material.ImageView;
 using Google.Android.Material.Shape;
+using Microsoft.Maui.Graphics;
 
 namespace Microsoft.Maui.Platform
 {
@@ -76,7 +77,9 @@ internal static void UpdateButtonStroke(this ShapeableImageView platformView, IB
 
 		internal static void UpdateButtonBackground(this ShapeableImageView platformView, IImageButton button)
 		{
-			platformView.UpdateMauiRippleDrawableBackground(button,
+			platformView.UpdateMauiRippleDrawableBackground(
+				button.Background ?? new SolidPaint(Colors.Transparent), // transparent to force some background
+				button,
 				beforeSet: () =>
 				{
 					// We have a background, so we need to remove the things that were set on the

src/Core/src/Platform/Android/MauiRippleDrawableExtensions.cs

@@ -50,14 +50,13 @@ internal static bool UpdateMauiRippleDrawableStroke(this AView platformView, IBu
 		return true;
 	}
 
-	internal static void UpdateMauiRippleDrawableBackground<TButton>(this AView platformView, TButton button,
+	internal static void UpdateMauiRippleDrawableBackground(this AView platformView,
+		Paint? background,
+		IButtonStroke stroke,
 		Func<int?>? getEmptyBackgroundColor = null,
 		Func<ColorStateList?>? getDefaultRippleColor = null,
 		Action? beforeSet = null)
-		where TButton : IButtonStroke, IView
 	{
-		var background = button.Background;
-
 		// Get the current background
 		var recreateRipple = false;
 		if (!platformView.TryGetMauiBackground(out var rippleDrawable, out var layerDrawable, out _, out var strokeDrawable, out _))
@@ -74,7 +73,7 @@ internal static void UpdateMauiRippleDrawableBackground<TButton>(this AView plat
 			recreateRipple = true;
 		}
 
-		var (width, color, radius) = button.GetStrokeProperties(platformView.Context!, false);
+		var (width, color, radius) = stroke.GetStrokeProperties(platformView.Context!, false);
 
 		// The previous background may have had transparency or a gradient which cannot
 		// be un-set, so we need an entirely new drawable.
@@ -132,7 +131,7 @@ internal static void UpdateMauiRippleDrawableBackground<TButton>(this AView plat
 			// Create the stroke layer.
 			strokeDrawable = new GradientDrawable();
 			strokeDrawable.SetCornerRadius(radius);
-			var strokeColor = button.StrokeColor ?? Colors.Black;
+			var strokeColor = stroke.StrokeColor ?? Colors.Black;
 			var strokeColorList = ColorStateListExtensions.CreateButton(strokeColor.ToPlatform());
 			strokeDrawable.SetStroke(width, strokeColorList);