MathJax Plugin: Propose MathJax 3 support

[Enquier]

What is the purpose of this pull request?

Allow users to select Mathjax v3 as the version for the math

Does your PR contain necessary tests?

All patches that change the editor code must include tests. You can always read more on PR testing, how to set the testing environment and how to create tests in the official CKEditor documentation.

This PR contains

• [ X] Unit tests
• [X ] Manual tests

Did you follow the CKEditor 4 code style guide?

Your code should follow the guidelines from the CKEditor 4 code style guide which helps keep the entire codebase consistent.

• [ X] PR is consistent with the code style guide

What is the proposed changelog entry for this pull request?

* [#3411](https://github.com/ckeditor/ckeditor4/issues/3411): A config option was added for the mathjax plugin to allow the user to select and use MathJax v3. The necessary code was added to the widget to enable use of v3.

What changes did you make?

-Added code to the widget that will execute correctly using V3, added config option to specify

Which issues does your PR resolve?

Closes #3411.

[Enquier]

@Comandeer I updated based on your feedback. Let me know if there are any other concerns you have

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It's been a while since we last heard from you. We are marking this pull request as stale due to inactivity. Please provide the requested feedback or the pull request will be closed after next 7 days.

[github-actions[bot]]

There was no activity regarding this pull request in the last 14 days. We're closing it for now. Still, feel free to provide us with requested feedback so that we can reopen it.