[Editor] fix highlighting disappearing when updating CodeMirror

[solkaz]

Description

This PR ensures that highlighting in the CodeMirror instance does not vanish when updating the instance. It checks if the props that update the CodeMirror instance have changed and sets a state variable

Motivation and Context

Fixes #564

Checklist:

• [x] My code follows the code style of this project.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Browsers

• [x] Chrome
• [x] Firefox
• [x] Safari
• [ ] Mobile:
• [ ] Other: