wayland-server: Track input_device resource for focused surface

We no long track the focused surface, but expect the compositor to set
focus when the focus changes.  We do track the resource for the input
device that corresponds to the current surface, in case that goes away.

src/wayland-server.c

diff --git a/src/wayland-server.c b/src/wayland-server.c
index 2295efc..4cb3dd5 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -342,7 +342,7 @@
 		container_of(listener, struct wl_input_device,
 			     pointer_focus_listener);
 
-	wl_input_device_set_pointer_focus(device, NULL, time, 0, 0, 0, 0);
+	device->pointer_focus_resource = NULL;
 }
 
 static void
@@ -353,7 +353,7 @@
 		container_of(listener, struct wl_input_device,
 			     keyboard_focus_listener);
 
-	wl_input_device_set_keyboard_focus(device, NULL, time);
+	device->keyboard_focus_resource = NULL;
 }
 
 WL_EXPORT void
@@ -412,7 +412,7 @@
 		wl_resource_post_event(resource,
 				       WL_INPUT_DEVICE_POINTER_FOCUS,
 				       time, surface, x, y, sx, sy);
-		wl_list_insert(surface->resource.destroy_listener_list.prev,
+		wl_list_insert(resource->destroy_listener_list.prev,
 			       &device->pointer_focus_listener.link);
 	}
 
@@ -445,7 +445,7 @@
 		wl_resource_post_event(resource,
 				       WL_INPUT_DEVICE_KEYBOARD_FOCUS,
 				       time, surface, &device->keys);
-		wl_list_insert(surface->resource.destroy_listener_list.prev,
+		wl_list_insert(resource->destroy_listener_list.prev,
 			       &device->keyboard_focus_listener.link);
 	}