title: how to implement debouncer for events with 'onEvent'?
body: <p><code>transformEvents</code> method will be removed in bloc version 8, and we should use <code>onEvent</code> method instead of, how can we implement <code>debounce</code> for events with <code>onEvent</code>?</p>
  <pre class="lang-dart prettyprint-override"><code>  @override
    Stream&lt;Transition&lt;PriceProposalEvent, PriceProposalState&gt;&gt; transformEvents(
      Stream&lt;PriceProposalEvent&gt; events,
      TransitionFunction&lt;PriceProposalEvent, PriceProposalState&gt; transitionFn,
    ) =&gt;
        super.transformEvents(
          events.debounceTime(const Duration(milliseconds: 200)),
          transitionFn,
        );
  </code></pre>