getinfo: CURLINFO_QUEUE_TIME_T

Returns the time, in microseconds, during which this transfer was held
in a waiting queue before it started "for real". A transfer might be put
in a queue if after getting started, it cannot create a new connection
etc due to set conditions and limits imposed by the application.

Ref: #12293
Closes #12368

lib/multi.c

@@ -1943,6 +1943,7 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
       }
 
       if(!result) {
+        *nowp = Curl_pgrsTime(data, TIMER_POSTQUEUE);
         if(async)
           /* We're now waiting for an asynchronous name lookup */
           multistate(data, MSTATE_RESOLVING);