[gtkmm] Gtk::StackSwitcher: Add TODO comments about Orientable

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 847ef3bec16c098b2c1e1fe895236e589ebbfc58
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri Jun 4 19:17:48 2021 +0200

    Gtk::StackSwitcher: Add TODO comments about Orientable
    
    Implement the Orientable interface when we can break ABI.
    GtkStackSwitcher now implements GtkOrientable.

 gtk/src/stackswitcher.hg | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/gtk/src/stackswitcher.hg b/gtk/src/stackswitcher.hg
index 38704d01..368bc14b 100644
--- a/gtk/src/stackswitcher.hg
+++ b/gtk/src/stackswitcher.hg
@@ -18,6 +18,7 @@
 
 #include <gtkmm/widget.h>
 #include <gtkmm/stack.h>
+//TODO: When we can break ABI: #include <gtkmm/orientable.h>
 
 _DEFS(gtkmm,gtk)
 _PINCLUDE(gtkmm/private/widget_p.h)
@@ -38,9 +39,10 @@ namespace Gtk
  * @ingroup Widgets
  * @newin{3,10}
  */
-class GTKMM_API StackSwitcher : public Widget
+class GTKMM_API StackSwitcher : public Widget //TODO: When we can break ABI: public Orientable
 {
   _CLASS_GTKOBJECT(StackSwitcher, GtkStackSwitcher, GTK_STACK_SWITCHER, Gtk::Widget, GtkWidget, , , 
GTKMM_API)
+  //TODO: When we can break ABI: _IMPLEMENTS_INTERFACE(Orientable)
 public:
   _CTOR_DEFAULT