Add Async image loading

Examples/Animating Views And Transitions/Complete/Landmarks/Landmarks/LandmarkDetail.swift

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+/*
+See LICENSE folder for this sample’s licensing information.
+
+Abstract:
+A view showing the details for a landmark.
+*/
+
+import SwiftUI
+
+struct LandmarkDetail: View {
+    @EnvironmentObject var userData: UserData
+    var landmark: Landmark
+    
+    var landmarkIndex: Int {
+        userData.landmarks.firstIndex(where: { $0.id == landmark.id })!
+    }
+    
+    var body: some View {
+        VStack {
+            MapView(coordinate: landmark.locationCoordinate)
+                .edgesIgnoringSafeArea(.top)
+                .frame(height: 300)
+            
+            CircleImage(image: landmark.image(forSize: 250))
+                .offset(x: 0, y: -130)
+                .padding(.bottom, -130)
+            
+            VStack(alignment: .leading) {
+                HStack {
+                    Text(verbatim: landmark.name)
+                        .font(.title)
+                    
+                    Button(action: {
+                        self.userData.landmarks[self.landmarkIndex]
+                            .isFavorite.toggle()
+                    }) {
+                        if self.userData.landmarks[self.landmarkIndex]
+                            .isFavorite {
+                            Image(systemName: "star.fill")
+                                .foregroundColor(Color.yellow)
+                        } else {
+                            Image(systemName: "star")
+                                .foregroundColor(Color.gray)
+                        }
+                    }
+                }
+                
+                HStack(alignment: .top) {
+                    Text(verbatim: landmark.park)
+                        .font(.subheadline)
+                    Spacer()
+                    Text(verbatim: landmark.state)
+                        .font(.subheadline)
+                }
+            }
+            .padding()
+            
+            Spacer()
+        }
+    }
+}
+
+#if DEBUG
+struct LandmarkDetail_Preview: PreviewProvider {
+    static var previews: some View {
+        let userData = UserData()
+        return LandmarkDetail(landmark: userData.landmarks[0])
+            .environmentObject(userData)
+    }
+}
+#endif