Use correct object for the aim slider bonus (#36216)

Currently the slider bonus works on the assumption that the travel
velocity of the previous slider is a part of the current object's
difficulty because it is part of the movement from prev to curr.
However, this is contradicted by the fact that `currVelocity` is a
combination of prev->curr + curr slider velocity and is actually
breaking the assumption that slider difficulty is contained in the
slider itself that we take when calculating difficult slider strains.

This makes it so that the slider bonus difficulty is contained in the
slider itself instead of buffing the next object, which makes both the
calculation overall more consistent and the slider factor calculation
actually work as expected.

Aim multiplier got slightly lowered because this change makes most of
the sliders gain a little bit

---------

Co-authored-by: James Wilson <tsunyoku@gmail.com>

osu.Game.Rulesets.Osu/Difficulty/Evaluators/AimEvaluator.cs

@@ -143,10 +143,10 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Evaluators
                 velocityChangeBonus *= Math.Pow(Math.Min(osuCurrObj.AdjustedDeltaTime, osuLastObj.AdjustedDeltaTime) / Math.Max(osuCurrObj.AdjustedDeltaTime, osuLastObj.AdjustedDeltaTime), 2);
             }
 
-            if (osuLastObj.BaseObject is Slider)
+            if (osuCurrObj.BaseObject is Slider)
             {
                 // Reward sliders based on velocity.
-                sliderBonus = osuLastObj.TravelDistance / osuLastObj.TravelTime;
+                sliderBonus = osuCurrObj.TravelDistance / osuCurrObj.TravelTime;
             }
 
             aimStrain += wiggleBonus * wiggle_multiplier;

osu.Game.Rulesets.Osu/Difficulty/Skills/Aim.cs

@@ -28,7 +28,7 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Skills
 
         private double currentStrain;
 
-        private double skillMultiplier => 26.7;
+        private double skillMultiplier => 26.6;
         private double strainDecayBase => 0.15;
 
         private readonly List<double> sliderStrains = new List<double>();