Docs: Various corrections and improvements to inline docs and docblocks.

See #57840


git-svn-id: https://develop.svn.wordpress.org/trunk@55753 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment.php

@@ -2981,6 +2981,7 @@ function do_all_trackbacks() {
  * @global wpdb $wpdb WordPress database abstraction object.
  *
  * @param int|WP_Post $post Post ID or object to do trackbacks on.
+ * @return void|false Returns false on failure.
  */
 function do_trackbacks( $post ) {
 	global $wpdb;