Refactor explain vulnerability drawer into its own component

What does this MR do and why?

In the beginning the Explain Vulnerability feature was simple, but as time went on we added more and more features. We've been breaking out each feature into its own separate component (explain_vulnerability_prompt.vue, explain_vulnerability_user_feedback.vue), but the drawer that shows the AI response is still part of the parent explain_vulnerability.vue. This MR breaks out the drawer as well into its own separate component. This is a refactor with no UI or behavior changes.

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 #420745 (closed)