Add highlight color to reply form if comment is highlighted

What does this MR do and why?

This MR adds the highlight color to the reply form (top) if a comment is highlighted (similar to what we have in place for internal notes).

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open a MR/Issue (e.g. http://gdk.test:3000/flightjs/Flight/-/merge_requests/3)
2. Add a comment
3. Copy link to comment
4. Open link
5. Reply to that highlighted comment
6. Check the reply form's top spacing

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.