Improve horizontal scrolling in wxRibbonControl.

Scroll by entire "sections", i.e. panes of the ribbon, instead of scrolling by
a fixed number of pixels as it's much more useful and user-friendly to uncover
the next section entirely instead of asking the user to press on the arrow
several times before being able to use it.

Closes #15232.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74068 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/ribbon/page.h

@@ -56,6 +56,7 @@ public:
     virtual bool Layout();
     virtual bool ScrollLines(int lines);
     bool ScrollPixels(int pixels);
+    bool ScrollSections(int sections);
 
     wxOrientation GetMajorAxis() const;