launcher: Move activate_session abstraction into the launcher code

login1 has a separate ActivateSession request, so put it here so
that we don't have to modify any backend code.

src/backends/native/meta-backend-native.c

@@ -221,7 +221,7 @@ meta_activate_session (void)
   MetaBackendNative *native = META_BACKEND_NATIVE (backend);
   MetaBackendNativePrivate *priv = meta_backend_native_get_instance_private (native);
 
-  if (!meta_launcher_activate_vt (priv->launcher, -1, &error))
+  if (!meta_launcher_activate_session (priv->launcher, &error))
     {
       g_warning ("Could not activate session: %s\n", error->message);
       g_error_free (error);

src/backends/native/meta-launcher.c

@@ -394,6 +394,13 @@ meta_launcher_free (MetaLauncher *launcher)
   g_slice_free (MetaLauncher, launcher);
 }
 
+gboolean
+meta_launcher_activate_session (MetaLauncher  *launcher,
+                                GError       **error)
+{
+  return meta_launcher_activate_vt (launcher, -1, error);
+}
+
 gboolean
 meta_launcher_activate_vt (MetaLauncher  *launcher,
 			   signed char    vt,
@@ -406,4 +413,3 @@ meta_launcher_activate_vt (MetaLauncher  *launcher,
 
   return send_message_to_wl (launcher, &message, sizeof (message), NULL, NULL, error);
 }
-

src/backends/native/meta-launcher.h

@@ -27,7 +27,11 @@ typedef struct _MetaLauncher MetaLauncher;
 MetaLauncher     *meta_launcher_new                     (void);
 void              meta_launcher_free                    (MetaLauncher  *self);
 
+gboolean          meta_launcher_activate_session        (MetaLauncher  *self,
+							 GError       **error);
+
 gboolean          meta_launcher_activate_vt             (MetaLauncher  *self,
 							 signed char    vt,
 							 GError       **error);
+
 #endif /* META_LAUNCHER_H */