Upsert queries can now use unique / primary key constraints composed of multiple fields

Upsert database queries can now be used on tables with unique/primary keys composed of multiple fields.

For this purpose, a new \Drupal\Core\Database\Query\Upsert::keyColumns() method was added, and \Drupal\Core\Database\Query\Upsert::key() has been deprecated.

Usage example for a table with a composite primary key on the collection and name columns:

    $this->connection->upsert($this->table)
      ->key(['collection', 'name'])
      ->fields([
        'collection' => $collection,
        'name' => $key,
        'value' => $value,
      ])
      ->execute();