Simplify GTK+ 2 version checks with a helper function

Use wx_is_at_least_gtk2(minor) instead of gtk_check_version(2, minor)
because it is more clear and also works as expected (i.e. returns true)
when using GTK+ 3 instead of creating difficult to notice bugs in the
code by failing the version check in this case.

See #18004.

src/gtk/anybutton.cpp

@@ -389,9 +389,7 @@ void wxAnyButton::DoSetBitmap(const wxBitmap& bitmap, State which)
 void wxAnyButton::DoSetBitmapPosition(wxDirection dir)
 {
 #ifdef __WXGTK210__
-#ifndef __WXGTK3__
-    if ( !gtk_check_version(2,10,0) )
-#endif
+    if ( wx_is_at_least_gtk2(10) )
     {
         GtkPositionType gtkpos;
         switch ( dir )