Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56523

Correctly updates the URL without overwriting parameters
Reloads the diff file content without reloading the page

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/58852, https://gitlab.com/gitlab-org/gitlab-ce/issues/42597

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52916

- Compare versions header is full width except in the unified diff mode
with no tree sidebar
  - Bar is always full width, but the content within stays centered when
unified and no tree sidebar
- File header is the same height as the "Compare versions header"
- aligns with the design system grid guidelines => 56px
- Diff file headers use a button group, switch icon order to open file
externally being the last option, all buttons will become icon buttons
(icon delivery by @dimitrieh)
- If a file header becomes sticky no rounded corner/double border
problem is visible anymore

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53139

Mousetrap is used as the help-tool to listen to keystrokes

Added currentDiffIndex getter to store that holds
the index of currently active diff file in the list

Instead of computing it on the component, we will take advantage of it
being available for all components in DiffsApp

Testing keyboard navigation and jumpToFile()

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51857

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53304

The empty state now only gets shown when no files exist in the branch.
If the user is reviewing 2 versions with no files, we don't show the state.

Refactors the diff app spec to use Vue test utils.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/48635

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53019

This caused many pain points when working with it.
Part of the data was camel cased the other snake case.
Other parts where snake case & then getting converted in components,
this conversion has the potential for leaking memory.

This changes that & makes it consistent with what it returned from the
API, snake case.

This improves the initial rendering performance of notes
by only creating a new TaskList for the whole app,
rather than on a per-note component basis.

This re-implements image commenting in merge request diffs.
This feature was previously lost when the merge request
page was refactored into Vue.

With this, we create an overlay component. The overlay
component handles displaying the comment badges
and the comment form badge.
Badges are displayed based on the position attribute
sent with the discussion.

Comment forms for diff files are controlled through
a different state property. This is so we don't
tie comment forms to diff files directly creating
deep nested state. Instead we create a flat array
which holds the file hash & the X & Y position of
the comment form.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/48956

This fixes a bug where a discussion on a none changed line
would not get fully removed and therefore leave the comment row
empty. This was caused by the discussiob being added
to the right when it shouldnt of been

This also fixes a very rare edge case where discussions would get added
twice to diff lines causing a Vue rendering warning

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53317

Also fixed a bug where discussions wouldn't be assigned to a line
when switching from discussion tab to changes tab

Pre-request to https://gitlab.com/gitlab-org/gitlab-ce/issues/48956

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

Detailed: Because of rewire we need to export a default empty object in our actions to prevent it to export the wrong default in karma. Vuex getters are global, and because the Vuex store uses several non namespaced moduled, there was already a getter named default, due to the same empty export.
In order to solve it I chose to namespace the module. Could also be fixed by importing the getters explicitly instead of all of them.