Resolve "Admin/Overview/Users mobile view"
## What does this MR do?
Fixes mobile layout issues on `/admin/users` page.
* Fixes control element placement when long usernames or email addresses overflow their container
* Fixes condensed dropdown menu (issue caused by acde2e30)
Before:
After:
## Are there points in the code the reviewer needs to double check?
Ensure css changes don't have any side effects elsewhere in GitLab. (I don't think they would...)
## Does this MR meet the acceptance criteria?
- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- Tests
- [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
## What are the relevant issue numbers?
Closes#22746
See merge request !7087
