Ensure Code Intelligence works with Highlight.js

What does this MR do and why?

As part of Highlighting source code using Highlight.js we need to ensure that Code Intelligence works with Highlight.js

Related to #345814 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. Enable the :highlight_js feature flag
2. Enable Code Intelligence (Docs)
3. Open a file for which Code Intelligence is enabled

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.