sway/ipc-json: add ext-foreign-toplevel-handle identifier to get_tree ipc output

Fixes #8291

sway/ipc-json.c

@@ -6,6 +6,7 @@
 #include <wlr/config.h>
 #include <wlr/types/wlr_content_type_v1.h>
 #include <wlr/types/wlr_output.h>
+#include <wlr/types/wlr_ext_foreign_toplevel_list_v1.h>
 #include <xkbcommon/xkbcommon.h>
 #include "config.h"
 #include "log.h"
@@ -577,6 +578,10 @@ static void ipc_json_describe_view(struct sway_container *c, json_object *object
 	json_object_object_add(object, "app_id",
 			app_id ? json_object_new_string(app_id) : NULL);
 
+	json_object_object_add(object, "foreign_toplevel_identifier",
+		c->view->ext_foreign_toplevel ?
+			json_object_new_string(c->view->ext_foreign_toplevel->identifier) : NULL);
+
 	bool visible = view_is_visible(c->view);
 	json_object_object_add(object, "visible", json_object_new_boolean(visible));
 

sway/sway-ipc.7.scd

@@ -389,6 +389,9 @@ node and will have the following properties:
 |- pid
 :  integer
 :  (Only views) The PID of the application that owns the view
+|- foreign_toplevel_identifier
+:  string
+:  (Only views) The ext-foreign-toplevel-list-v1 toplevel identifier of this node.
 |- visible
 :  boolean
 :  (Only views) Whether the node is visible