[5.x] Support arguments in user can/cant tags

[jacksleight]

This PR adds support for passing additional arguments to gates via the {{ user:can }}/{{ user:cant }} tags.

Gate::define('view secret', function ($user, $secret) {
    return $user->hasAccessToSecret($secret);
});

{{ user:can do="view secret" secret="foo" }}
    ...
{{ /user:can }}