Add JuiceStreamPath to allow editing JuiceStream in catch editor

A `JuiceStream` holds a legacy `SliderPath` as the representation of the path.
However, the `SliderPath` representation is difficult to work with because `SliderPath` works in 2D position, while osu!catch works in `(time, x)` coordinates.
This `JuiceStreamPath` represents the path in a more convenient way, a polyline connecting list of `(distance, x)` vertices.

osu.Game.Rulesets.Catch/Objects/JuiceStreamPathVertex.cs

@@ -0,0 +1,33 @@
+// 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;
+
+#nullable enable
+
+namespace osu.Game.Rulesets.Catch.Objects
+{
+    /// <summary>
+    /// A vertex of a <see cref="JuiceStreamPath"/>.
+    /// </summary>
+    public readonly struct JuiceStreamPathVertex : IComparable<JuiceStreamPathVertex>
+    {
+        public readonly double Distance;
+
+        public readonly float X;
+
+        public JuiceStreamPathVertex(double distance, float x)
+        {
+            Distance = distance;
+            X = x;
+        }
+
+        public int CompareTo(JuiceStreamPathVertex other)
+        {
+            int c = Distance.CompareTo(other.Distance);
+            return c != 0 ? c : X.CompareTo(other.X);
+        }
+
+        public override string ToString() => $"({Distance}, {X})";
+    }
+}