Added $request_port and $is_request_port variables.

Added $request_port and $is_request_port variables.

The $request_port variable contains the port passed by the client in the
request line (for HTTP/1.x) or ":authority" pseudo-header (for HTTP/2 and
HTTP/3).  If the request line contains no host, or ":authority" is missing,
then $request_port is taken from the "Host" header, similar to the $host
variable.

The $is_request_port variable contains ":" if $request_port is non-empty,
and is empty otherwise.