Fix for parsing attribute options labels, when & used.

[bartoszkubicki]

Description

After updating Magento to 2.2.6 when attribute is saved, and option label contains & label is cut before &. It is caused by usage of function parse_str() which is confused by &

Fixed Issues (if relevant)

Manual testing scenarios

1. Add attribute option with label containing char &
2. Save attribute
3. Check if label wa correctly saved.

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 @sidolov, thank you for the review.
ENGCOM-3081 has been created to process this Pull Request

[sidolov]

Hi @bartoszkubicki , please, create the PR with the same fixes to 2.3-develop branch, we are focusing on the 2.3 release line for now and current PR will be merged as port for 2.3-develop.
Thank you!

[magento-engcom-team]

Hi @bartoszkubicki. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.