Coding Standards: Use static closures when not using $this.

When a closure does not use `$this`, it can be made `static` for improved performance.

Static closures are supported in PHP since PHP 5.4. ​

Props jrf, hellofromTonya, swissspidy, SergeyBiryukov.
See #53359.
Built from https://develop.svn.wordpress.org/trunk@51657


git-svn-id: http://core.svn.wordpress.org/trunk@51263 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api.php

@@ -3227,7 +3227,7 @@ function rest_get_endpoint_args_for_schema( $schema, $method = WP_REST_Server::C
 function rest_convert_error_to_response( $error ) {
 	$status = array_reduce(
 		$error->get_all_error_data(),
-		function ( $status, $error_data ) {
+		static function ( $status, $error_data ) {
 			return is_array( $error_data ) && isset( $error_data['status'] ) ? $error_data['status'] : $status;
 		},
 		500