Fix build

Author: jfversluis

src/Plugin.Maui.FormsMigration/SecureStorage/KeyChain.ios.cs

@@ -1,3 +1,4 @@
+using Foundation;
 using Security;
 
 namespace Plugin.Maui.FormsMigration;

src/Plugin.Maui.FormsMigration/VersionTracking/LegacyPreferences.android.cs

@@ -85,7 +85,7 @@ static T PlatformGet<T>(string key, T defaultValue, string sharedName)
 
 	static ISharedPreferences GetSharedPreferences(string sharedName)
 	{
-		var context = Application.Context;
+		var context = Platform.AppContext;
 
 		return string.IsNullOrWhiteSpace(sharedName) ?
 #pragma warning disable CS0618 // Type or member is obsolete

src/Plugin.Maui.FormsMigration/VersionTracking/LegacyPreferences.ios.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using Foundation;
 
 namespace Plugin.Maui.FormsMigration;