Clarify security report findings in merge request widget

What does this MR do?

• Removes ❌ and ✅ icons from security report items
• Adds new component that renders a grouped list of report items (groups: New and Fixed)
• Fixes spacing issue between report items on smaller screens

Screenshots

before	after

Screencaptures

before	after
security_reports_before	security_reports_after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Related to #214329 (closed)