- Add a `destroy_user` ability. This didn't exist before, and was implicit in
  other abilities (only admins could access the admin area, so only they could
  destroy all users; a user can only access their own account page, and so can
  destroy only themselves).

- Grant this ability to admins, and when the current user is trying to destroy
  themselves. Disallow destroying ghost users in all cases.

- Modify the `Users::DestroyService` to check this ability. Also check it in
  views to decide whether or not to show the "Delete User" button.

- Add a short summary of the Ghost User to the bio.

Rather than using a separate `ghost` state. This lets us have the benefits of
both ghost and blocked users (ghost: true, state: blocked) without having to
rewrite a number of queries to include cases for `state: ghost`.

Todo done clicking is kind of unusable.

Closes #25465

See merge request !8691

The Done button will change to an Undo button and the line item will be greyed out.
Bold links will be unbolded.
The user can undo the task by clicking the Undo button.

* master: (313 commits)
  Allow slashes in slash command arguments
  Add API endpoint to get all milestone merge requests
  remove trailing comma
  Restore pagination to admin abuse reports
  replace deprecated NoErrorsPlugin with NoEmitOnErrorsPlugin
  only compress assets in production
  Reduce number of pipelines created to test pagination
  add CHANGELOG.md entry for !8761
  prevent diff unfolding link from appearing for deleted files
  fix build failures
  only show diff unfolding link if there are more lines to show
  fix typo in node section
  Only yield valid references in ReferenceFilter.references_in
  Cache js selectors; fix css
  move "Install node modules" step before "Migrate DB" within update process
  Renders pagination again for pipelines table
  update migration docs for 8.17 to include minimum node version
  Add CHANGELOG file
  Fix positioning of top scroll button
  Remove comments in migration
  ...

Adding links to user & build stage in a Build message

Closes #26500

See merge request !8641

Fix for XSS vulnerability in SVG attachments

See https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2059

* Alter wiki_pages factory with custom creation operation