Add availability annotations

Package.swift

@@ -5,9 +5,6 @@ import PackageDescription
 
 let package = Package(
   name: "UIPreview",
-  platforms: [
-    .iOS(.v13)
-  ],
   products: [
     // Products define the executables and libraries a package produces, and make them visible to other packages.
     .library(

Sources/UIPreview/Binding+Mock.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13, *)
 extension Binding {
   public static func mock(_ value: Value) -> Self {
     var value = value

Sources/UIPreview/Demo.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13, *)
 struct ContentView: View {
   var body: some View {
     Text("Hello, world!")
@@ -7,6 +8,7 @@ struct ContentView: View {
   }
 }
 
+@available(iOS 13, *)
 struct ContentView_Previews: PreviewProvider {
   static var previews: some View {
     ContentView()
@@ -14,6 +16,7 @@ struct ContentView_Previews: PreviewProvider {
   }
 }
 
+@available(iOS 13, *)
 struct Demo_Previews: PreviewProvider {
   static var previews: some View {
     Group {

Sources/UIPreview/ForEach+Raw.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13, *)
 extension ForEach where Data.Element: Hashable, ID == Data.Element, Content: View {
   init(values: Data, content: @escaping (Data.Element) -> Content) {
     self.init(values, id: \.self, content: content)

Sources/UIPreview/PreviewColorScheme.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13, *)
 extension View {
   public func previewLightTheme() -> some View {
     ColorSchemePreview(scheme: .light) { self }
@@ -10,12 +11,14 @@ extension View {
   }
 }
 
+@available(iOS 13, *)
 extension ColorScheme {
   var previewName: String {
     String(describing: self).capitalized
   }
 }
 
+@available(iOS 13, *)
 struct ColorSchemePreview<Preview: View>: View {
   private let preview: Preview
   private let scheme: ColorScheme

Sources/UIPreview/PreviewComponent.swift

@@ -1,12 +1,13 @@
 import SwiftUI
 
+@available(iOS 13, *)
 extension View {
   public func previewAsComponent() -> some View {
     ComponentPreview(component: self)
   }
 }
 
-
+@available(iOS 13, *)
 extension ContentSizeCategory {
   static let smallestAndLargest = [allCases.first!, allCases.last!]
 
@@ -15,6 +16,7 @@ extension ContentSizeCategory {
   }
 }
 
+@available(iOS 13, *)
 struct ComponentPreview<Component: View>: View {
   var component: Component
 

Sources/UIPreview/PreviewScreen.swift

@@ -10,12 +10,14 @@ public let defaultDeviceNames: [String] =
     "iPad Pro (12.9-inch) (4th generation)"
   ]
 
+@available(iOS 13, *)
 extension View {
   public func previewAsScreen(deviceNames: [String] = defaultDeviceNames) -> some View {
     ScreenPreview(screen: self, deviceNames: deviceNames)
   }
 }
 
+@available(iOS 13, *)
 struct ScreenPreview<Screen: View>: View {
   var screen: Screen
   var deviceNames: [String]