Improve editor selection rotation value wrapping

This fixes two issues the previous algorithm had:
1.  A half-turn rotation used to show up as -180°.
2.  Rotating more than 180° in one drag event would overwhelm it
    and cause the value to go outside its range.

This comes at the cost of a negligible performance hit,
since a division (modulo) is performed instead of just addition/subtraction.

osu.Game/Screens/Edit/Compose/Components/SelectionBoxRotationHandle.cs

@@ -134,10 +134,7 @@ namespace osu.Game.Screens.Edit.Compose.Components
                 cumulativeRotation.Value = rawCumulativeRotation;
             }
 
-            if (cumulativeRotation.Value < -180)
-                cumulativeRotation.Value += 360;
-            else if (cumulativeRotation.Value > 180)
-                cumulativeRotation.Value -= 360;
+            cumulativeRotation.Value = (cumulativeRotation.Value - 180) % 360 + 180;
 
             HandleRotate?.Invoke((float)cumulativeRotation.Value - oldRotation);
         }