Add Alt+MouseWheel as a global volume adjust binding

This offers the defaults users have come to expect while also allowing
rebinding (if they don't want it) and better compatibility with other
global actions (since this is no longer implemented using `OnScroll`
event flow).

Addresses part of ppy#31267.

osu.Game/Input/Bindings/GlobalActionContainer.cs

@@ -209,7 +209,9 @@ public static IEnumerable<GlobalAction> GetGlobalActionsFor(GlobalActionCategory
         private static IEnumerable<KeyBinding> audioControlKeyBindings => new[]
         {
             new KeyBinding(new[] { InputKey.Alt, InputKey.Up }, GlobalAction.IncreaseVolume),
+            new KeyBinding(new[] { InputKey.Alt, InputKey.MouseWheelUp }, GlobalAction.IncreaseVolume),
             new KeyBinding(new[] { InputKey.Alt, InputKey.Down }, GlobalAction.DecreaseVolume),
+            new KeyBinding(new[] { InputKey.Alt, InputKey.MouseWheelDown }, GlobalAction.DecreaseVolume),
 
             new KeyBinding(new[] { InputKey.Alt, InputKey.Left }, GlobalAction.PreviousVolumeMeter),
             new KeyBinding(new[] { InputKey.Alt, InputKey.Right }, GlobalAction.NextVolumeMeter),