Make GtkOverlayLayout public

Keeping the layout manager type private does not
really work when it has layout child properties
that need to be usable in ui files.

gtk/gtk.h

@@ -164,6 +164,7 @@
 #include <gtk/gtknotebook.h>
 #include <gtk/gtkorientable.h>
 #include <gtk/gtkoverlay.h>
+#include <gtk/gtkoverlaylayout.h>
 #include <gtk/gtkpadcontroller.h>
 #include <gtk/gtkpagesetup.h>
 #include <gtk/gtkpaned.h>

gtk/gtkoverlay.c

@@ -22,7 +22,7 @@
 
 #include "gtkoverlay.h"
 
-#include "gtkoverlaylayoutprivate.h"
+#include "gtkoverlaylayout.h"
 #include "gtkbuildable.h"
 #include "gtkintl.h"
 #include "gtkmarshalers.h"

gtk/gtkoverlaylayout.c

@@ -20,7 +20,7 @@
 
 #include "config.h"
 
-#include "gtkoverlaylayoutprivate.h"
+#include "gtkoverlaylayout.h"
 
 #include "gtkintl.h"
 #include "gtklayoutchild.h"