Userland: Add horizontal mouse scroll support

Author: https://github.com/can3p
Commit: 1662213737
Pull-request: https://github.com/SerenityOS/serenity/pull/11246
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibGUI/Slider.cpp

@@ -139,7 +139,7 @@ void Slider::mouseup_event(MouseEvent& event)
 void Slider::mousewheel_event(MouseEvent& event)
 {
     auto acceleration_modifier = step();
-    auto wheel_delta = event.wheel_delta();
+    auto wheel_delta = event.wheel_delta_y();
 
     if (event.modifiers() == KeyModifier::Mod_Ctrl)
         acceleration_modifier *= 6;