Feature summary (what you would like to be able to do and where):

Have CodeMirror-based syntax highlighting for SRT and WebVTT subtitle files when editing TimedText pages.

Use case(s) and Benefits (Describe the actual underlying problem which you want to solve. Why should this be implemented? Do not describe only
a solution):

TimedText subtitle files are currently edited as plain, unstyled text in the standard wikitext editor textarea, even though their syntax can be rather complex and easy to make mistakes in. It is also a format that most editors will not be super familiar with. This makes it hard to spot common authoring mistakes

It would be useful to identify mistakes before attempting a save and failing on the validation step.