title: Google Play Billing Library: Determine base plan / expiry of subscription purchase
body: <p>I am using the Google Play Billing Library 5 and have a <em>subscription</em> product with different <em>base plans</em>.</p>
  <p>When processing the purchases in the <code>PurchasesUpdatedListener</code> or in the callback of <code>queryPurchasesAsync</code>, I receive a list of <code>Purchase</code> objects which contain inter alia the product IDs, purchase time and whether it's auto-renewing.</p>
  <p>But how do I know which <em>base plan</em> was selected by the user, and when it expires?</p>
  <p>The <code>PurchaseHistoryRecord</code> returned from <code>queryPurchaseHistoryAsync</code> also seems  not to contain this info.</p>
  <p>I know the Play Developer API returns the expiry time
  with <code>purchases.subscriptionsv2.get</code>, but is the inconvenience of using the API directly necessary?</p>