ui/console: add console event notifier infrastructure

Add a NotifierList to DisplayState so display backends can be notified
when consoles are added or removed at runtime.

No events are fired yet, that follows in the next commits.

Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260623-b4-ui-v4-23-4656aec3398d@redhat.com>

ui/console.c

@@ -70,6 +70,7 @@ struct DisplayState {
     bool refreshing;
 
     QLIST_HEAD(, DisplayChangeListener) listeners;
+    NotifierList console_notifiers;
 };
 
 static DisplayState *display_state;
@@ -84,6 +85,16 @@ static bool console_compatible_with(QemuConsole *con,
 static QemuConsole *qemu_graphic_console_lookup_unused(void);
 static void dpy_set_ui_info_timer(void *opaque);
 
+void qemu_console_notify(QemuConsoleEventType type, QemuConsole *con)
+{
+    DisplayState *ds = get_alloc_displaystate();
+    QemuConsoleEvent event = {
+        .type = type,
+        .con = con,
+    };
+    notifier_list_notify(&ds->console_notifiers, &event);
+}
+
 static void gui_update(void *opaque)
 {
     uint64_t interval = GUI_REFRESH_INTERVAL_IDLE;
@@ -1056,10 +1067,22 @@ static DisplayState *get_alloc_displaystate(void)
 {
     if (!display_state) {
         display_state = g_new0(DisplayState, 1);
+        notifier_list_init(&display_state->console_notifiers);
     }
     return display_state;
 }
 
+void qemu_console_add_notifier(Notifier *notifier)
+{
+    DisplayState *ds = get_alloc_displaystate();
+    notifier_list_add(&ds->console_notifiers, notifier);
+}
+
+void qemu_console_remove_notifier(Notifier *notifier)
+{
+    notifier_remove(notifier);
+}
+
 /*
  * Called by main(), after creating QemuConsoles
  * and before initializing ui (sdl/vnc/...).