[Forwardport] Fixes updating wishlist item if an item object is passed instead its id.

[eduard13]

Description

Original PR #16372

This PR fixes removing the wishlist item from wishlist while updating it, if instead of id it is sent \Magento\Wishlist\Model\Item object.

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 @eduard13. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
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[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-2130 has been created to process this Pull Request

[sidolov]

@magento-engcom-team give me test instance

[magento-engcom-team]

Hi @sidolov. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @sidolov, here is your new Magento instance.
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[magento-engcom-team]

Hi @eduard13. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.