Move online metrics out of BeatmapSetInfo model

osu.Game/Beatmaps/IBeatmapOnlineInfo.cs

@@ -0,0 +1,17 @@
+// 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.
+
+#nullable enable
+
+namespace osu.Game.Beatmaps
+{
+    /// <summary>
+    /// Beatmap info retrieved for previewing locally.
+    /// </summary>
+    public interface IBeatmapOnlineInfo
+    {
+        int? MaxCombo { get; }
+
+        BeatmapMetrics? Metrics { get; }
+    }
+}