Fix FieldItemList stub and missing ItemList stub

Author: mglaman

stubs/Drupal/Core/Field/FieldItemList.stub

@@ -4,12 +4,17 @@ namespace Drupal\Core\Field;
 
 use Drupal\Core\TypedData\Plugin\DataType\ItemList;
 
+/**
+ * @template T of \Drupal\Core\Field\FieldItemInterface
+ * @extends ItemList<T>
+ * @implements FieldItemListInterface<T>
+ */
 class FieldItemList extends ItemList implements FieldItemListInterface {
 
   /**
    * @return \Drupal\Core\Field\FieldItemInterface
    */
-  protected function createItem($offset = 0, $value = NULL): \Drupal\Core\Field\FieldItemInterface {
+  protected function createItem(int $offset = 0, ?mixed $value = NULL): \Drupal\Core\Field\FieldItemInterface {
   }
 
 }

stubs/Drupal/Core/TypedData/Plugin/DataType/ItemList.stub

@@ -0,0 +1,16 @@
+<?php
+
+namespace Drupal\Core\TypedData\Plugin\DataType;
+
+use Drupal\Core\TypedData\ComplexDataInterface;
+use Drupal\Core\TypedData\ListInterface;
+use Drupal\Core\TypedData\TypedData;
+use Drupal\Core\TypedData\TypedDataInterface;
+
+/**
+ * @template T of TypedDataInterface
+ * @implements \IteratorAggregate<int, T>
+ * @implements ListInterface<T>
+ */
+class ItemList extends TypedData implements \IteratorAggregate, ListInterface {
+}