WIP: Resolve "Show link to full list of vulnerabilities for Container Scanning and DAST in the MR widget"

What does this MR do?

Removes the "Show complete code vulnerabilities report" links from the MR page and replaces them with a top-level button (see screenshots).

NOTE: This has been marked as WIP to prevent accidental merging. Merging this before the CE changes have been back-ported could have undesired side effects. Please review as normal, but DO NOT MERGE

Why was this MR needed?

To unify the way we display reports on the MR page.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5239 (closed)