EscapingFunctionsTrait: add esc_xml() to the list of escaping functions

This function was introduced in WP 5.5.

As it's been around for about three years now, I'm not going to special case it with a version check.

Ref: https://core.trac.wordpress.org/ticket/50117

Fixes 1937

Author: jrfnl

WordPress/Helpers/EscapingFunctionsTrait.php

@@ -71,6 +71,7 @@ trait EscapingFunctionsTrait {
 		'esc_textarea'               => true,
 		'esc_url_raw'                => true,
 		'esc_url'                    => true,
+		'esc_xml'                    => true,
 		'filter_input'               => true,
 		'filter_var'                 => true,
 		'floatval'                   => true,