Separate slider body to bypass snaking logic

The snaking logic contains a lot of caching/optimisations and offsetting of the path which is tedious to re-compute when the path changes.

osu.Game.Rulesets.Osu/Objects/Drawables/Pieces/ManualSliderBody.cs

@@ -0,0 +1,20 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Collections.Generic;
+using OpenTK;
+
+namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
+{
+    /// <summary>
+    /// A <see cref="SliderBody"/> with the ability to set the drawn vertices manually.
+    /// </summary>
+    public class ManualSliderBody : SliderBody
+    {
+        public new void SetVertices(IReadOnlyList<Vector2> vertices)
+        {
+            base.SetVertices(vertices);
+            Size = Path.Size;
+        }
+    }
+}