mod_proxy: Restore ap_proxy_transfer_between_connections().

mod_proxy: Restore ap_proxy_transfer_between_connections().

* modules/proxy/mod_proxy.h:
  Restore the interface of ap_proxy_transfer_between_connections() back to
  before MMN 20210506.0.
  Add ap_proxy_tunnel_conn_bytes_in() and ap_proxy_tunnel_conn_bytes_out().
  New proxy_tunnel_conn_t typedef'ed from opaque struct proxy_tunnel_conn.

* modules/proxy/mod_proxy.h(ap_proxy_tunnel_conn_get_read,
                            ap_proxy_tunnel_conn_get_transferred):
  Axed/replaced by ap_proxy_tunnel_conn_bytes_in() and
  ap_proxy_tunnel_conn_bytes_out().

* modules/proxy/proxy_util.c(struct proxy_tunnel_conn):
  Replace "exchanged" by "bytes_in" and "bytes_out".

* modules/proxy/proxy_util.c(proxy_transfer):
  New helper implementing ap_proxy_transfer_between_connections() and
  returning both &bytes_in and &bytes_out.

* modules/proxy/proxy_util.c(ap_proxy_transfer_between_connections):
  Now calls proxy_transfer().

* modules/proxy/proxy_util.c(ap_proxy_tunnel_conn_bytes_in,
                             ap_proxy_tunnel_conn_bytes_out):
  Return tc->bytes_in and tc->bytes_out respectively.

* modules/proxy/proxy_util.c(proxy_tunnel_forward):
  Use proxy_transfer() which updates in->bytes_in, &out->bytes_out.
  tunnel->replied will be updated in proxy_tunnel_run().

* modules/proxy/proxy_util.c(proxy_tunnel_forward):
  Fall through the "done" label in any case to set tunnel->replied based
  on tunnel->client->bytes_out > 0.

* modules/proxy/mod_proxy_http.c(ap_proxy_http_process_response):
  Use ap_proxy_tunnel_conn_bytes_{in,out}() for worker->s->{read,transferred}
  accounting.

* modules/proxy/mod_proxy_http.c(proxy_http_async_finish):
  Update worker->s->{read,transferred} when async too.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1893594 13f79535-47bb-0310-9956-ffa450edef68