Add basic realm models

Only the file related ones are really required outside of tests, but
seems like as good an opportunity as ever to get the rest of the models
into the game project.

osu.Game/Models/RealmNamedFileUsage.cs

@@ -0,0 +1,32 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using JetBrains.Annotations;
+using osu.Game.Database;
+using osu.Game.IO;
+using Realms;
+
+#nullable enable
+
+namespace osu.Game.Models
+{
+    public class RealmNamedFileUsage : EmbeddedObject, INamedFile, INamedFileUsage
+    {
+        public RealmFile File { get; set; } = null!;
+
+        public string Filename { get; set; } = null!;
+
+        public RealmNamedFileUsage(RealmFile file, string filename)
+        {
+            File = file;
+            Filename = filename;
+        }
+
+        [UsedImplicitly]
+        private RealmNamedFileUsage()
+        {
+        }
+
+        IFileInfo INamedFileUsage.File => File;
+    }
+}