Add example Unity Project

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/GroupTrack.cs

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+using System;
+using System.Collections.Generic;
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    /// <summary>
+    /// A group track is a container that allows tracks to be arranged in a hierarchical manner.
+    /// </summary>
+    [Serializable]
+    [TrackClipType(typeof(TrackAsset))]
+    [SupportsChildTracks]
+    public class GroupTrack : TrackAsset
+    {
+        internal override bool CanCompileClips()
+        {
+            return false;
+        }
+
+        /// <inheritdoc />
+        public override IEnumerable<PlayableBinding> outputs
+        {
+            get { return PlayableBinding.None; }
+        }
+    }
+}