title: Open matAutocomplete with open openPanel() method
body: <p>I'm working with Angular Material's <a href="https://material.angular.io/components/autocomplete/overview" rel="noreferrer"><strong>matAutocomplete</strong></a> component, and according to the <a href="https://material.angular.io/components/autocomplete/api#MatAutocompleteTrigger" rel="noreferrer">docs</a>, there is a method which can open/close an autocomplete panel with a openPanel()/closePanel() method. Any suggestion to how can I integrate it into already working example?</p>
  
  <p>Here is a what I did with <a href="https://stackblitz.com/edit/angular-acfyxt?embed=1&amp;file=app/autocomplete-filter-example.html" rel="noreferrer">live example</a> while trying to implement the feature.</p>