Docs: Add a comment about the $title global usage in various admin files.

This should make it clear that the variable is used as part of the HTML `<title>` tag on admin screens.

Props ravipatel, hellofromTonya, sabernhardt, audrasjb, SergeyBiryukov.
Fixes #53729.
Built from https://develop.svn.wordpress.org/trunk@51475


git-svn-id: http://core.svn.wordpress.org/trunk@51086 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/admin.php

@@ -334,9 +334,10 @@ if ( isset( $plugin_page ) ) {
 	 */
 	do_action( "load-importer-{$importer}" ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 
+	// Used in the HTML title tag.
+	$title        = __( 'Import' );
 	$parent_file  = 'tools.php';
 	$submenu_file = 'import.php';
-	$title        = __( 'Import' );
 
 	if ( ! isset( $_GET['noheader'] ) ) {
 		require_once ABSPATH . 'wp-admin/admin-header.php';