Create a shared project with all Win App common files (8.1 and 10)

Finally use the dependency injected Resource Service

WinAppCommon/Common/Constants.cs

@@ -0,0 +1,15 @@
+namespace ModernKeePass.Common
+{
+    public class Constants
+    {
+        public class File
+        {
+            public static int OneMegaByte => 1048576;
+        }
+
+        public class Settings
+        {
+            public static string SaveSuspend => nameof(SaveSuspend);
+        }
+    }
+}