15863: [Forwardport] Refactored javascript code of admin notification modal popup

[IvanPletnyov]

Description

Refactored code in popup.phtml and popup.js

Original pull request

15341 [Backport] Refactored javascript code of admin notification modal popup

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-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @IvanPletnyov. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

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[VladimirZaets]

Hi @IvanPletnyov , please, sign CLA, otherwise, we can't process your pull request

[magento-engcom-team]

Hi @sidolov, thank you for the review.
ENGCOM-2039 has been created to process this Pull Request

[magento-engcom-team]

@IvanPletnyov thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[magento-engcom-team]

Hi @IvanPletnyov. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.6 release.

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