title: Swift Get URLSessionDataTask start time / current operation time
body: <p>I have a <code>URLSessionDataTask</code> instance and I would like to know when the operation started (a <code>Date</code> object) so I can calculate how much time has elapsed.</p>
  
  <p>I've found <code>URLSessionTaskTransactionMetrics</code> in Apple's documentation (<a href="https://developer.apple.com/documentation/foundation/urlsessiontasktransactionmetrics#declarations" rel="nofollow noreferrer">https://developer.apple.com/documentation/foundation/urlsessiontasktransactionmetrics#declarations</a>) but this does not show how to get the <code>transactionMetrics</code> property, unless I'm missing something obvious.</p>