How is a quote's `ext_shipping_info` property implemented and used?

[dmitry_fedyuk (Dmitrii Fediuk)]

magento/magento2/blob/910ca337/app/code/Magento/Quote/etc/db_schema.xml#L89-L89

magento/magento2/blob/910ca337/app/code/Magento/Quote/Model/Quote.php#L92-L93

It is never used by the built-in Magento 2 modules.