Core/Movement: Implement initializing parabolic splines using jump gravity instead of max parabolic height

Port From (https://github.com/TrinityCore/TrinityCore/commit/684cd9d9681466019dcd06ad6f994890cff8cb2e)

Source/Game/Movement/MoveSplineInitArgs.cs

@@ -42,6 +42,7 @@ namespace Game.Movement
         public int path_Idx_offset;
         public float velocity;
         public float parabolic_amplitude;
+        public float vertical_acceleration;
         public float time_perc;
         public uint splineId;
         public float initialOrientation;