Work item UI improvements

What does this MR do and why?

Implement most of the feedback from discussions on #363613 (closed)

Tweak appearance of Task modals on issue descriptions

• more padding
• more space around title
• horizontal layout for status field

Screenshots or screen recordings

How to set up and validate locally

1. Enable work_items feature flag
2. Create (or edit) an issue. Add a checklist item to the description
3. Hover the checklist item > Create work item
4. Create the work item and click the title to edit
5. Change title or status
6. See title of the task change in issue description after next realtime_changes update

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.