[dotnet] Enable nullability in template projects. (#12118)

And fix any warnings that came up.

dotnet/Templates/Microsoft.MacCatalyst.Templates/maccatalyst/AppDelegate.cs

@@ -4,7 +4,7 @@ using UIKit;
 namespace MacCatalystApp1 {
 	[Register ("AppDelegate")]
 	public class AppDelegate : UIApplicationDelegate {
-		public override UIWindow Window {
+		public override UIWindow? Window {
 			get;
 			set;
 		}
@@ -16,7 +16,7 @@ namespace MacCatalystApp1 {
 
 			// create a UIViewController with a single UILabel
 			var vc = new UIViewController ();
-			vc.View.AddSubview (new UILabel (Window.Frame) {
+			vc.View!.AddSubview (new UILabel (Window!.Frame) {
 				BackgroundColor = UIColor.White,
 				TextAlignment = UITextAlignment.Center,
 				Text = "Hello, Catalyst!"

dotnet/Templates/Microsoft.MacCatalyst.Templates/maccatalyst/MacCatalystApp1.csproj

@@ -4,5 +4,6 @@
     <RuntimeIdentifier>maccatalyst-x64</RuntimeIdentifier>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">MacCatalystApp1</RootNamespace>
     <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>

dotnet/Templates/Microsoft.MacCatalyst.Templates/maccatalyst/SceneDelegate.cs

@@ -6,7 +6,7 @@ namespace MacCatalystApp1 {
 	public class SceneDelegate : UIResponder, IUIWindowSceneDelegate {
 
 		[Export ("window")]
-		public UIWindow Window { get; set; }
+		public UIWindow? Window { get; set; }
 
 		[Export ("scene:willConnectToSession:options:")]
 		public void WillConnect (UIScene scene, UISceneSession session, UISceneConnectionOptions connectionOptions)

dotnet/Templates/Microsoft.iOS.Templates/ios/AppDelegate.cs

@@ -4,7 +4,7 @@ using UIKit;
 namespace iOSApp1 {
 	[Register ("AppDelegate")]
 	public class AppDelegate : UIApplicationDelegate {
-		public override UIWindow Window {
+		public override UIWindow? Window {
 			get;
 			set;
 		}
@@ -16,7 +16,7 @@ namespace iOSApp1 {
 
 			// create a UIViewController with a single UILabel
 			var vc = new UIViewController ();
-			vc.View.AddSubview (new UILabel (Window.Frame) {
+			vc.View!.AddSubview (new UILabel (Window!.Frame) {
 				BackgroundColor = UIColor.White,
 				TextAlignment = UITextAlignment.Center,
 				Text = "Hello, iOS!"

dotnet/Templates/Microsoft.iOS.Templates/ios/SceneDelegate.cs

@@ -6,7 +6,7 @@ namespace iOSApp1 {
 	public class SceneDelegate : UIResponder, IUIWindowSceneDelegate {
 
 		[Export ("window")]
-		public UIWindow Window { get; set; }
+		public UIWindow? Window { get; set; }
 
 		[Export ("scene:willConnectToSession:options:")]
 		public void WillConnect (UIScene scene, UISceneSession session, UISceneConnectionOptions connectionOptions)

dotnet/Templates/Microsoft.iOS.Templates/ios/iOSApp1.csproj

@@ -3,5 +3,6 @@
     <TargetFramework>net6.0-ios</TargetFramework>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">iOSApp1</RootNamespace>
     <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>

dotnet/Templates/Microsoft.iOS.Templates/ioslib/iOSLib1.csproj

@@ -2,5 +2,6 @@
   <PropertyGroup>
     <TargetFramework>net6.0-ios</TargetFramework>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">iOSLib1</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>

dotnet/Templates/Microsoft.macOS.Templates/macos/macOSApp1.csproj

@@ -3,5 +3,6 @@
     <TargetFramework>net6.0-macos</TargetFramework>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">macOSApp1</RootNamespace>
     <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>

dotnet/Templates/Microsoft.tvOS.Templates/tvos/AppDelegate.cs

@@ -4,7 +4,7 @@ using UIKit;
 namespace tvOSApp1 {
 	[Register ("AppDelegate")]
 	public class AppDelegate : UIApplicationDelegate {
-		public override UIWindow Window {
+		public override UIWindow? Window {
 			get;
 			set;
 		}

dotnet/Templates/Microsoft.tvOS.Templates/tvos/tvOSApp1.csproj

@@ -3,5 +3,6 @@
     <TargetFramework>net6.0-tvos</TargetFramework>
     <RootNamespace Condition="'$(name)' != '$(name{-VALUE-FORMS-}safe_namespace)'">tvOSApp1</RootNamespace>
     <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>