GitLab

This file tree displays all the diff files in a tree like format
Each file is taken and converted into a tree with folders
Each folder can be toggled open & closed
Clicking a file will scroll to the diff file & highlight with a glow affect

Searching the tree list will search only files & return a list of the
files without any folders

Each file row contains an icon to show changed, new file or deleted
Each row will also contain the added & removed lines count

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14249

Display `formatter` as the sole content of `position` object.
This means `diff_file` data is not referenced, which is the
caseu of "IOError: not opened for reading".

Every browser which supports IntersectionObserver will now use it over
observing scroll and resize events. Older browsers without support fall
back on the previous behavior.

Additionally the MutationObserver can be enabled and disabled manually
via the helper method `startContentObserver` and `stopContentObserver`.
This might prove useful on pages where we manipulate the DOM
extensively.

**Why?**
- This is needed for the Web Terminal feature.
  https://gitlab.com/gitlab-org/gitlab-ee/issues/5426

**Notes:**
- Introduces a `pane` Vuex module.
- Some views should not be kept alive (i.e. job details).
  This is why a `keepAlive` flag was introduced for views.

Closes #51912

These changes are a backport from
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7411

Removes old mediator and service pattern and uses the new store.
Middle step before moving everything into one single vue app

**Why?**
- This is needed by the Web Terminal EE feature.
  https://gitlab.com/gitlab-org/gitlab-ee/issues/5426

**Notes:**
- RightPane component tabs is now data driven.

With the new Job Log page in Vue, we'll need to reuse the same functions for scrolling
that we're using in the jQuery one.
This page extracts that logic into reusable functions