24146 Add focus state to buttons and dropdowns

## What does this MR do?
Adds focus state to buttons and dropdowns

## Are there points in the code the reviewer needs to double check?
All focus states of buttons and dropdowns :)

## Why was this MR needed?
Improve accessibility

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-11-07_at_4.30.31_PM](/uploads/8db2ac5e225c78495797180faf7bdb28/Screen_Shot_2016-11-07_at_4.30.31_PM.png)
After:
![Screen_Shot_2016-11-07_at_4.30.16_PM](/uploads/4a81810cafe3063eef02b7bc87f8ce69/Screen_Shot_2016-11-07_at_4.30.16_PM.png)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #24146

See merge request !7347