[5.4] Preserve route parameters name

[themsaid]

As reported in: #18593

This PR ensures that the parameter keys are preserved so that if you override Illuminate\Routing\Controller@callAction in your controller the $parameters is an associative array,

public function callAction($method, $parameters)
{
    return call_user_func_array([$this, $method], $parameters);
}

This behaviour was broken in #17973, this PR should get back the original behaviour.

[frankdejonge]

Would probably be good to add the test-case from that issue too, as a guarantee for the future.