MDL-58048 mod: New callback implementation

* Callback function implementation of
<modname>_core_calendar_event_action_shows_item_count for:
 - mod_assign
 - mod_forum

Part of MDL-55611 epic.

mod/assign/lib.php

@@ -1772,3 +1772,20 @@ function mod_assign_core_calendar_provide_event_action(\core_calendar\event $eve
         $actionable
     );
 }
+
+/**
+ * Callback function that determines whether an action event should be showing its item count
+ * based on the event type and the item count.
+ *
+ * @param \core_calendar\event $event The calendar event.
+ * @param int $itemcount The item count associated with the action event.
+ * @return bool
+ */
+function mod_assign_core_calendar_event_action_shows_item_count(\core_calendar\event $event, $itemcount = 0) {
+    // List of event types where the action event's item count should be shown.
+    $eventtypesshowingitemcount = [
+        ASSIGN_EVENT_TYPE_GRADINGDUE
+    ];
+    // For mod_assign, item count should be shown if the event type is 'gradingdue' and there is one or more item count.
+    return in_array($event->eventtype, $eventtypesshowingitemcount) && $itemcount > 0;
+}