[AltWidget] Adopts containerBackground(for:) on iOS 17

AltWidget/Extensions/View+AltWidget.swift

@@ -0,0 +1,27 @@
+//
+//  View+AltWidget.swift
+//  AltStore
+//
+//  Created by Riley Testut on 8/18/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+import SwiftUI
+
+extension View
+{
+    @ViewBuilder
+    func widgetBackground(_ backgroundView: some View) -> some View
+    {
+        if #available(iOSApplicationExtension 17, *)
+        {
+            containerBackground(for: .widget) {
+                backgroundView
+            }
+        }
+        else
+        {
+            background(backgroundView)
+        }
+    }
+}