Docs: Add missing description for $comment global.

Props immeet94, mukesh27.
Fixes #46928. See #47110.

git-svn-id: https://develop.svn.wordpress.org/trunk@46391 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment.php

@@ -184,7 +184,7 @@ function get_approved_comments( $post_id, $args = array() ) {
  *
  * @since 2.0.0
  *
- * @global WP_Comment $comment
+ * @global WP_Comment $comment Global comment object.
  *
  * @param WP_Comment|string|int $comment Comment to retrieve.
  * @param string                $output  Optional. The required return type. One of OBJECT, ARRAY_A, or ARRAY_N, which correspond to