Allow fully qualified global constants

[asispts]

This PR will add support to fully qualified global constant. For example

use const PHP_URL_QUERY;

// 
var_dump(explode(DIRECTORY_SEPARATOR, __DIR__));
echo parse_url('localhost', PHP_URL_QUERY);

will be formatted to

var_dump(explode(\DIRECTORY_SEPARATOR, __DIR__));
echo parse_url('localhost', \PHP_URL_QUERY);

[asispts]

There is a bug in Slevomat coding standard. See slevomat/coding-standard#1621