Highlight across inserts

[Skaiir]

Describe the Bug

Currently when we interrupt some markdown with inserts, it breaks the underlying syntax tree and hence highlighting:

Fixing this is far from trivial, as we probably would have to invert the way we parse things, starting with the underlying language and then adding an overlay language mixin on top of it (described here).

However we definitely don't want that for the interpreter parser. So we'd need two mixed languages.

For now, I would advise against working on this.

Steps to Reproduce

1. npm run start
2. add some text with bold markdown tags
3. add an insert inside of those tags
4. the syntax highlighting breaks

Expected Behavior

4. Syntax highlighting should remain, and the new styles should just be painted on top.