Resolve "Report abusive content from an issue or merge request"

What does this MR do?

Adds "report abuse" toggle and button to issuables.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Issue, can edit, mobile

MR, can edit, mobile

Issue, can not edit, mobile

MR, can not edit, mobile

Issue, can not edit, desktop

MR, can not edit, desktop

Issue, can edit, desktop

MR, can edit, deskop

http://imgur.com/GyGbk4a (sorry for link, gif too big)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #30281 (closed)