Add initial implementation of editor clipboard

osu.Game/Screens/Edit/ClipboardContent.cs

@@ -0,0 +1,27 @@
+// 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 System.Collections.Generic;
+using System.Linq;
+using Newtonsoft.Json;
+using osu.Game.IO.Serialization;
+using osu.Game.IO.Serialization.Converters;
+using osu.Game.Rulesets.Objects;
+
+namespace osu.Game.Screens.Edit
+{
+    public class ClipboardContent : IJsonSerializable
+    {
+        [JsonConverter(typeof(TypedListConverter<HitObject>))]
+        public IList<HitObject> HitObjects;
+
+        public ClipboardContent()
+        {
+        }
+
+        public ClipboardContent(EditorBeatmap editorBeatmap)
+        {
+            HitObjects = editorBeatmap.SelectedHitObjects.ToList();
+        }
+    }
+}