API: Expose committer details for a commit

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22312

See merge request !7849

Resolve "Highlighting lines is broken"

## What does this MR do?

Add line highlighting back to diff view.  This was working in the MR "changes" tab, but not on a commit page such as https://gitlab.com/winniehell/reproduction-area/commit/9101e66f5761929002956e0f2dd65d7f8643903d

~~This MR also fixes the `scrollToElement` method in `MergeRequestTabs` to account for the extra height of the tab links which are now fixed in place once they are scrolled to the top of the screen.~~ (removed in favor of !7051)

This MR also refactors much of the `Diff` and `MergeRequestTabs` classes to es6 syntax in an effort to increase readability.

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

Check out both MR "change" tabs and commit diff pages and ensure that line highlighting works and that loading a page with one of these permalink hashes correctly highlights and scrolls to the line.

Ensure I didn't break anything in the transition to es6 syntax.  Check the functionality of the tabs on MR pages, as well as diff page interactivity (unfolding hidden lines in diff files, adding comments to diffs, etc).  I have checked these myself, but another set of eyes would be a good idea.

## 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 #23696

See merge request !7090

If SSH prototol is disabled don't say the user requires SSH keys

Closes #24921

See merge request !7840

Change ref property to commitRef

## What does this MR do?
Changes `ref` prop to `commitRef` because `ref` is a reserved word in Vue.js

## Does this MR meet the acceptance criteria?

- [x] [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
- [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)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #25264

//cc @selfup

See merge request !7901

Clean up common_utils.js

## What does this MR do?

- Remove unused functions from `common_utils.js`.
- Move functions which are used from only one file to that file.

## Why was this MR needed?

Because some utils weren't that common (anymore).

See merge request !7318

Fixes ActionView::Template::Error: undefined method `text?` for nil:NilClass

Closes #25251

See merge request !7893