Fix security dashboard errors on IE11

What does this MR do?

On Internet Explorer 11, the security dashboard does not load:

Here's what had to be done to fix the issue:

• Add Object.entries polyfill to prevent Object doesn't support property or method 'entries' error (done in CE: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28732)
• Ensure Sets are converted to Arrays to prevent [Vue warn]: Error in created hook: "TypeError: Invalid attempt to spread non-iterable instance"

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides
• Separation of EE specific content

Performance and testing

• Tested in all supported browsers