[ADD] Full-screen app screenshot preview

AltStore/Views/App Detail/AppScreenshotsPreview.swift

@@ -0,0 +1,69 @@
+//
+//  AppScreenshotsPreview.swift
+//  SideStore
+//
+//  Created by Fabian Thies on 23.12.22.
+//  Copyright © 2022 SideStore. All rights reserved.
+//
+
+import SwiftUI
+import AsyncImage
+import AltStoreCore
+
+struct AppScreenshotsPreview: View {
+    
+    @Environment(\.dismiss)
+    private var dismiss
+    
+    let urls: [URL]
+    let aspectRatio: CGFloat
+    @State var index: Int
+    
+    init(urls: [URL], aspectRatio: CGFloat = 9/16, initialIndex: Int = 0) {
+        self.urls = urls
+        self.aspectRatio = aspectRatio
+        self._index = State(initialValue: initialIndex)
+    }
+    
+    var body: some View {
+        TabView(selection: $index) {
+            ForEach(Array(urls.enumerated()), id: \.offset) { (i, url) in
+                AsyncImage(url: url) { image in
+                    image
+                        .resizable()
+                } placeholder: {
+                    Rectangle()
+                        .foregroundColor(Color(.secondarySystemBackground))
+                        .aspectRatio(aspectRatio, contentMode: .fill)
+                }
+                .aspectRatio(aspectRatio, contentMode: .fit)
+                .cornerRadius(8)
+                .padding()
+                .tag(i)
+            }
+        }
+        .tabViewStyle(PageTabViewStyle(indexDisplayMode: .never))
+        .toolbar {
+            ToolbarItem(placement: .navigationBarTrailing) {
+                SwiftUI.Button {
+                    self.dismiss()
+                } label: {
+                    Text("Close")
+                }
+            }
+        }
+    }
+}
+
+extension AppScreenshotsPreview: Equatable {
+    /// Prevent re-rendering of the view if the parameters didn't change
+    static func == (lhs: AppScreenshotsPreview, rhs: AppScreenshotsPreview) -> Bool {
+        lhs.urls == rhs.urls
+    }
+}
+
+//struct AppScreenshotsPreview_Previews: PreviewProvider {
+//    static var previews: some View {
+//        AppScreenshotsPreview()
+//    }
+//}