Description:
------------
After upgrading from PHP 5.4 to 7.2 (with OS upgrade) the behavior of json_encode with JSON_NUMERIC_CHECK changed.

In 5.4, a hex string was converted to an int.

In 7.2, a hex string is output as a hex string.

Test script:
---------------
$ php --version
PHP 5.4.45 (cli) (built: Oct 16 2015 11:02:47)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2014 Zend Technologies

$ php --interactive
php > print(json_encode("0xFF", JSON_NUMERIC_CHECK));
255

$ php --version
PHP 7.2.11 (cli) (built: Oct  9 2018 15:09:36) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies

$ php --interactive
Interactive shell

php > print(json_encode("0xFF", JSON_NUMERIC_CHECK));
"0xFF"