Make wxWindow::HasScrollbar() respect wxScrolled::ShowScrollbars().

Override CanScroll() in wxScrolled to return the real state of the scrollbar
instead of just relying on the wx[HV]SCROLL styles.

Closes #15440.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74714 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/scrolwin.h

@@ -29,6 +29,8 @@ public:
                                bool noRefresh = false);
     virtual void AdjustScrollbars();
 
+    virtual bool IsScrollbarShown(int orient) const;
+
 protected:
     virtual void DoScroll(int x, int y);
     virtual void DoShowScrollbars(wxScrollbarVisibility horz,