[Backport] Convert to string $option->getValue, in order to be compared with oth…

[mage2pratik]

Original Pull Request

#15720

#mm18it
…er saved options in previous cart items

Description

To decide whether a product with the same options is already present in the cart, magento makes a comparison with the string that represents the buyrequest in json format with those saved in the database. When a product is added by the Rest API the option code attribute encoded in the json is a number, whereas from the frontend context it is a string. In this case, this bufix forces the option attribute value in string, creating arrays that will later be converted into json

Fixed Issues (if relevant)

1. Configurable product addtocart with restAPI not working as expected #15028:Configurable product addtocart with restAPI not working as expected2. ...

Manual testing scenarios

Same test performed by issue writer

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-2730 has been created to process this Pull Request

[magento-engcom-team]

Hi @mage2pratik. Thank you for your contribution.
We will aim to release these changes as part of 2.1.16.
Please check the release notes for final confirmation.