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/LibVT/TerminalWidget.cpp

@@ -918,7 +918,7 @@ void TerminalWidget::mousewheel_event(GUI::MouseEvent& event)
     if (!is_scrollable())
         return;
     set_auto_scroll_direction(AutoScrollDirection::None);
-    m_scrollbar->increase_slider_by(event.wheel_delta() * scroll_length());
+    m_scrollbar->increase_slider_by(event.wheel_delta_y() * scroll_length());
     GUI::Frame::mousewheel_event(event);
 }