Added reviewer state icons

What does this MR do and why?

Added new icons for the new merge request reviewer states

Screenshots or screen recordings

How to set up and validate locally

• Enable mr_request_changes feature flag
• Visit a merge request
• Assign yourself as reviewer
• Start a new review
• Submit the review selecting different options
• Icon changes in sidebar

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.

#428090 (closed)