Replace the download, fork and resolve discussion in a new issue icons - EE

What does this MR do?

This is the EE counterpart for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15436

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15436