Issue #3349973 by Akram Khan, Arantxio, m.stenta, daffie, poker10, hestenet,...

  public function checkExtensions() {

    $connection = Database::getConnection();

    try {

      // Enable pg_trgm for PostgreSQL 13 or higher.

      // @todo Remove this if-statement in D11 when the minimum required version

      // for PostgreSQL becomes 13 or higher. https://www.drupal.org/i/3357409

      if (version_compare($connection->version(), '13.0', '>=')) {

        $connection->query('CREATE EXTENSION IF NOT EXISTS pg_trgm');

      }

      if ($connection->schema()->extensionExists('pg_trgm')) {

        $this->pass(t('PostgreSQL has the pg_trgm extension enabled.'));

      }