Add support for 451 http status code (Unavailable For Legal Reasons.)

Though this is technically still in the proposal stage, there is support from the core team and precedent in #16914

Props andizer.
Fixes #35333.


git-svn-id: https://develop.svn.wordpress.org/trunk@36273 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -1021,6 +1021,7 @@ function get_status_header_desc( $code ) {
 			428 => 'Precondition Required',
 			429 => 'Too Many Requests',
 			431 => 'Request Header Fields Too Large',
+			451 => 'Unavailable For Legal Reasons',
 
 			500 => 'Internal Server Error',
 			501 => 'Not Implemented',