Make BeatmapSetInfo equatable

osu.Game/Beatmaps/BeatmapSetInfo.cs

@@ -9,7 +9,7 @@ using osu.Game.Database;
 
 namespace osu.Game.Beatmaps
 {
-    public class BeatmapSetInfo : IHasPrimaryKey, IHasFiles<BeatmapSetFileInfo>, ISoftDelete
+    public class BeatmapSetInfo : IHasPrimaryKey, IHasFiles<BeatmapSetFileInfo>, ISoftDelete, IEquatable<BeatmapSetInfo>
     {
         public int ID { get; set; }
 
@@ -46,5 +46,7 @@ namespace osu.Game.Beatmaps
         public override string ToString() => Metadata?.ToString() ?? base.ToString();
 
         public bool Protected { get; set; }
+
+        public bool Equals(BeatmapSetInfo other) => OnlineBeatmapSetID == other?.OnlineBeatmapSetID;
     }
 }

osu.Game/Online/DownloadTrackingComposite.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Online
     /// A component which tracks a beatmap through potential download/import/deletion.
     /// </summary>
     public abstract class DownloadTrackingComposite<TModel, TModelManager> : CompositeDrawable
-        where TModel : class
+        where TModel : class, IEquatable<TModel>
         where TModelManager : class, IDownloadModelManager<TModel>
     {
         public readonly Bindable<TModel> ModelInfo = new Bindable<TModel>();