Docs: Clarify the file header summary for wp-includes/meta.php, the top-level file for the core Meta API.

Also adds inline DocBlocks for files broken out in #33413 and now brought in via `require_once()`.

See #33413. See #33701.


git-svn-id: https://develop.svn.wordpress.org/trunk@34407 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/meta.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * Metadata API
+ * Core Metadata API
  *
  * Functions for retrieving and manipulating metadata of various WordPress object types. Metadata
  * for an object is a represented by a simple key-value pair. Objects may contain multiple
@@ -11,5 +11,8 @@
  * @since 2.9.0
  */
 
+/** Core metdata functionality */
 require_once( ABSPATH . WPINC . '/meta-functions.php' );
+
+/** WP_Meta_Query class */
 require_once( ABSPATH . WPINC . '/class-wp-meta-query.php' );