Add Last changed date to search results
If someone is facing exactly same issue, Here is what i did. 

In my .theme file I've preprocessed search results like this

function YOURTHEME_preprocess_search_result(&amp;$variables){
  $result = $variables['result'];
  $info = array();
  if($result['node']){
    $info['date'] = format_date($result['node']->getChangedTime(),'short');
  }

$variables['info_split'] = $info;
  $variables['info']['#context'] = array(
    'info' => $info,
  );
}

After this the date will be available in info_split.date variable and it will be automatically rendered as in the twig file all the info is rendered you can optionally render o hide some parts of the search listing.