editor: added mathtype plugin to tinymce

[0einstein0]

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Description

Partially Closes #581

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings (for relevant code).
• I've followed the CSS/JS and React guidelines (for relevant code).
• I've followed the web accessibility guidelines (for relevant code).
• I've followed the user interface guidelines (for relevant code).
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).

Third-party code

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