Bump React Ace to v12

[RichDom2185]

Description

Supersedes #2880.

Also did a bit of cleanup.

Our custom syntax highlighting is still broken at the moment but other syntax highlighting works.

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
• [ ] Code quality improvements

How to test

Checklist

• [x] I have tested this code
• [ ] I have updated the documentation