Design comments visual update

What does this MR do and why?

Design comments visual update:

• Reduces the spacing used
• Updates the reply form to match the form styling of regular comments
• Fixes the border bottom radius of the reply function
• Uses gl-font-sm for the timestamp and the collapse/expand function

Follow-up to Fix styling and alignment of resolve design thr... (!123698 - merged)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open an issue (e.g. http://gdk.test:3000/flightjs/Flight/-/issues/38)
2. Upload a design
3. Add a comment to the design
4. Check the comment form

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.

Related to #411677 (comment 1403721944)+