Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/8195

Improve the renderign of new and existing discussions
by reducing the number of watchers on each object & array.
Previously every discussion change would trigger an update for every
discussion component.

Also tidied up some components to get them closer to our docs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51506

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 reverts commit a82a5957, reversing
changes made to e7df959b.

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

Un-commented out expect checks in mutation spec

This re-enables legacy diff notes on the merge request diffs
This feature was not workig correctly after the Vue refactor
LegacyDiffNotes have no `position`, instead they only have a `line_code`
As an extra, this also re-enables commenting on legacy diffs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/48873

Exports state to allow tests
Adds specs for the getters that didn't have any.