Optionally support using wxImageList in wxRibbonBar

This allows to avoid consuming too many bitmap resources.

Closes #18657.

include/wx/ribbon/buttonbar.h

@@ -213,6 +213,7 @@ protected:
     bool m_layouts_valid;
     bool m_lock_active_state;
     bool m_show_tooltips_for_disabled;
+    wxRibbonBar* m_ownerRibbonBar;
 
 #ifndef SWIG
     wxDECLARE_CLASS(wxRibbonButtonBar);