lib: transfer origin and proxy handling

Add `data->state.origin` as the origin the transfer is sending the
current request to/gets the response from. Use it for request specific
properties like authentication, hsts and cookie handling, etc.

Unless talking to a forwarding HTTP proxy (e.g. not tunneling),
`data->state.origin` and `conn->origin` are the same.

With a forwarding HTTP proxy in play, `conn->origin` is set to
`conn->http_proxy.peer` and `conn->bits.origin_is_proxy` (a new bit) is
set.

Remove the connection bits, now replaced with:

* `conn->bits.socksproxy` -> `conn->socks_proy.peer`
* `conn->bits.httpproxy` -> `conn->http_proy.peer`
* `conn->bits.proxy` -> `(conn->socks_proy.peer || conn->http_proy.peer`)
* `conn->bits.tunnel_proxy` -> (`conn->http_proy.peer && !conn->bits.origin_is_proxy`)
* `(conn->bits.httpproxy && !conn->bits.tunnel_proxy)` -> `conn->bits.origin_is_proxy`

Rename `noproxy.[ch]` to `proxy.[ch]`. Move the connection proxy setup
code from `url.c` to `proxy.c`.

Remove `data->info.conn_remote_port` as no one uses it.

Add test_40_02b for a SOCKS connection to a forwarding HTTPS proxy.

Update internal documentation about peers and creds.

Closes #21967

lib/cf-socket.c

@@ -1634,8 +1634,6 @@ static void cf_socket_update_data(struct Curl_cfilter *cf,
   if(cf->connected && (cf->sockindex == FIRSTSOCKET)) {
     struct cf_socket_ctx *ctx = cf->ctx;
     data->info.primary = ctx->ip;
-    /* not sure if this is redundant... */
-    data->info.conn_remote_port = cf->conn->origin->port;
   }
 }