Add a missing file header to wp-includes/class-wp-customize-widgets.php, separate out the class DocBlock for `WP_Customize_Widgets`.

Fixes #31446.


git-svn-id: https://develop.svn.wordpress.org/trunk@31544 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-widgets.php

@@ -1,13 +1,21 @@
 <?php
 /**
- * Customize Widgets Class
- *
- * Implements widget management in the Customizer.
+ * WordPress Customize Widgets classes
  *
  * @package WordPress
  * @subpackage Customize
  * @since 3.9.0
  */
+
+/**
+ * Customize Widgets class.
+ *
+ * Implements widget management in the Customizer.
+ *
+ * @since 3.9.0
+ *
+ * @see WP_Customize_Manager
+ */
 final class WP_Customize_Widgets {
 
 	/**