QWaylandWindow: Add surfaceRoleCreated/Destroyed signals

There are many APIs in Wayland that require a surface role to be
assigned (e.g. XDG Toplevel) before they can be used, where
the surfaceCreated() signal is too early.

Change-Id: I400a6279f21554267259f812a2efb33451b4709b
Reviewed-by: Vlad Zahorodnii <vlad.zahorodnii@kde.org>

src/gui/kernel/qplatformwindow_p.h

@@ -126,6 +126,8 @@ public:
 Q_SIGNALS:
     void surfaceCreated();
     void surfaceDestroyed();
+    void surfaceRoleCreated();
+    void surfaceRoleDestroyed();
     void xdgActivationTokenCreated(const QString &token);
 
 protected: