无法获取完整协议的URL

$request->url()和$request->fullUrl()均无法获取完整协议头的URL,建议新增方法完善,示例:
`
/**
* @return string
*/
public function protocol()
{
return $this->scheme() . '://';
}

/**
* @return string
*/
public function scheme()
{
return strtolower($this->header('x-forwarded-proto', 'http'));
}
`

Start from the request methods referenced in the issue, $request->url() and $request->fullUrl(), and compare them with the proposed protocol() and scheme() behavior. The work is done when a request can expose a complete URL including its protocol, including the forwarded-protocol case described in the issue.

Written by the indexing model from the issue text.