Fix time snap of sliders not matching when SV is not 1.0x

This regressed with https://github.com/ppy/osu/pull/20850 because the
function was used in other places which expect it to factor slider
velocity into the equation.

Rather than reverting, I've added a new argument, as based on the method
naming alone it was hard to discern whether SV should actually be
considered.

The reason for the change in #20850 was to avoid the SV coming in from a
reference object which may not have a correct SV in the first place. In
such cases, passing `false` to the function will give the expected
behaviour.

osu.Game.Tests/Visual/Editing/TestSceneDistanceSnapGrid.cs

@@ -193,7 +193,7 @@ namespace osu.Game.Tests.Visual.Editing
 
             IBindable<double> IDistanceSnapProvider.DistanceSpacingMultiplier => DistanceSpacingMultiplier;
 
-            public float GetBeatSnapDistanceAt(HitObject referenceObject) => beat_snap_distance;
+            public float GetBeatSnapDistanceAt(HitObject referenceObject, bool useReferenceSliderVelocity = true) => beat_snap_distance;
 
             public float DurationToDistance(HitObject referenceObject, double duration) => (float)duration;