API Add method to get foreign class key on polymorphic has_many

src/ORM/PolymorphicHasManyList.php

@@ -29,6 +29,14 @@ class PolymorphicHasManyList extends HasManyList
         return $this->dataQuery->getQueryParam('Foreign.Class');
     }
 
+    /**
+     * Gets the field name which holds the related object class.
+     */
+    public function getForeignClassKey(): string
+    {
+        return $this->classForeignKey;
+    }
+
     /**
      * Create a new PolymorphicHasManyList relation list.
      *