Drupal 8 with Oracle Database

/**
 * Detects all supported databases that are compiled into PHP.
 *
 * @return
 *   An array of database types compiled into PHP.
 */
function drupal_detect_database_types() {
  $databases = drupal_get_database_types();

  foreach ($databases as $driver => $installer) {
    $databases[$driver] = $installer->name();
  }

  return $databases;
}

/**
 * Returns all supported database driver installer objects.
 *
 * @return \Drupal\Core\Database\Install\Tasks[]
 *   An array of available database driver installer objects.
 */
function drupal_get_database_types() {
  $databases = [];
  $drivers = [];

  // The internal database driver name is any valid PHP identifier.
  $mask = '/^' . DRUPAL_PHP_FUNCTION_PATTERN . '$/';
  $files = file_scan_directory(DRUPAL_ROOT . '/core/lib/Drupal/Core/Database/Driver', $mask, ['recurse' => FALSE]);
  if (is_dir(DRUPAL_ROOT . '/drivers/lib/Drupal/Driver/Database')) {
    $files += file_scan_directory(DRUPAL_ROOT . '/drivers/lib/Drupal/Driver/Database/', $mask, ['recurse' => FALSE]);
  }
  foreach ($files as $file) {
    if (file_exists($file->uri . '/Install/Tasks.php')) {
      $drivers[$file->filename] = $file->uri;
    }
  }
  foreach ($drivers as $driver => $file) {
    $installer = db_installer_object($driver);
    if ($installer->installable()) {
      $databases[$driver] = $installer;
    }
  }

  // Usability: unconditionally put the MySQL driver on top.
  if (isset($databases['mysql'])) {
    $mysql_database = $databases['mysql'];
    unset($databases['mysql']);
    $databases = ['mysql' => $mysql_database] + $databases;
  }

  return $databases;
}

Looks like it should detect the driver automatically, provided it is placed correctly. Don't think the location mentioned with oracle driver is correct. See the 2 folders scanned for drivers. The mask is just filtering proper names (defined in bootstrap.inc). It does need an Install/Tasks.php to be recognized.

CORRECTION: The oracle driver mentions the second path in the script. Looks like that is the path for non-core drivers.

Note that the Database server must be up and running. The creation of the database obviously needs the proper permissions and should use the options desired for Drupal or look at settings to allow custom ones. There is something like init_commands on the $database that could be used.