Add support for horizontal mouse wheel scrolling in wxSTC.

Handle horizontal mouse wheel scrolling events in a similar (but simpler, as
they always scroll and never change the font size) way to the vertical ones in
wxStyledTextCtrl.

Closes #15266.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74312 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/stc/stc.cpp

@@ -4695,9 +4695,11 @@ void wxStyledTextCtrl::OnContextMenu(wxContextMenuEvent& evt) {
 
 void wxStyledTextCtrl::OnMouseWheel(wxMouseEvent& evt)
 {
-    m_swx->DoMouseWheel(evt.GetWheelRotation(),
+    m_swx->DoMouseWheel(evt.GetWheelAxis(),
+                        evt.GetWheelRotation(),
                         evt.GetWheelDelta(),
                         evt.GetLinesPerAction(),
+                        evt.GetColumnsPerAction(),
                         evt.ControlDown(),
                         evt.IsPageScroll());
 }