divide wheel deltas by 50.

src/Avalonia.Windowing/WindowImpl.cs

@@ -179,7 +179,7 @@ namespace Avalonia.Windowing
                     break;
 
                 case MouseEventType.Wheel:
-                    Input(new RawMouseWheelEventArgs(MouseDevice, (uint)Environment.TickCount, _inputRoot, new Point(_lastPosition.X, _lastPosition.Y), new Point(evt.Position.X, evt.Position.Y), InputModifiers.None));
+                    Input(new RawMouseWheelEventArgs(MouseDevice, (uint)Environment.TickCount, _inputRoot, new Point(_lastPosition.X, _lastPosition.Y), new Point(evt.Position.X / 50, evt.Position.Y / 50), InputModifiers.None));
                     return;
             }