Add missing doc blocks to wp-admin/includes/*.

Fix some egregious uses of tabbing.
Some functions can simply return `apply_filters(...)` instead of setting a variable that is immediately returned.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32654 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/install.php

@@ -52,6 +52,8 @@ $step = isset( $_GET['step'] ) ? (int) $_GET['step'] : 0;
  * Display install header.
  *
  * @since 2.5.0
+ *
+ * @param string $body_classes
  */
 function display_header( $body_classes = '' ) {
 	header( 'Content-Type: text/html; charset=utf-8' );
@@ -82,6 +84,8 @@ function display_header( $body_classes = '' ) {
  * Display installer setup form.
  *
  * @since 2.8.0
+ *
+ * @param string|null $error
  */
 function display_setup_form( $error = null ) {
 	global $wpdb;