docs: add ComponentSystem.id (#8087)

Author: aidinabedi

src/framework/components/system.js

@@ -15,6 +15,14 @@ import { Vec4 } from '../../core/math/vec4.js';
  * type.
  */
 class ComponentSystem extends EventHandler {
+    /**
+     * The id type of the ComponentSystem.
+     *
+     * @type {string}
+     * @readonly
+     */
+    id;
+
     /**
      * Create a new ComponentSystem instance.
      *