window-switcher: add age order to window cycling

- Add a new configuration option to control the window switcher
  traversal order.

- Document cycle windows behavior with new option `order` in
  `<windowSwitcher>`

include/config/rcxml.h

@@ -185,6 +185,7 @@ struct rcxml {
 		enum cycle_osd_style style;
 		enum cycle_osd_output_criteria output_criteria;
 		char *thumbnail_label_format;
+		enum window_switcher_order order;
 	} window_switcher;
 
 	struct wl_list window_rules; /* struct window_rule.link */

include/config/types.h

@@ -107,6 +107,11 @@ enum lab_window_type {
 	LAB_WINDOW_TYPE_LEN
 };
 
+enum window_switcher_order {
+	WINDOW_SWITCHER_ORDER_FOCUS,
+	WINDOW_SWITCHER_ORDER_AGE,
+};
+
 enum cycle_osd_style {
 	CYCLE_OSD_STYLE_CLASSIC,
 	CYCLE_OSD_STYLE_THUMBNAIL,

include/labwc.h

@@ -188,6 +188,7 @@ struct server {
 	struct wl_listener xdg_toplevel_icon_set_icon;
 
 	struct wl_list views;
+	uint64_t next_view_creation_iid;
 	struct wl_list unmanaged_surfaces;
 
 	struct seat seat;

include/view.h

@@ -174,6 +174,7 @@ struct view {
 
 	bool mapped;
 	bool been_mapped;
+	uint64_t creation_iid;
 	enum lab_ssd_mode ssd_mode;
 	enum ssd_preference ssd_preference;
 	bool shaded;