This reverts commit a82a5957, reversing
changes made to e7df959b.

Enables frozens string for the following:

* lib/gitlab/conflict/**/*.rb
* lib/gitlab/cross_project_access/**/*.rb
* lib/gitlab/cycle_analytics/**/*.rb
* lib/gitlab/data_builder/**/*.rb
* lib/gitlab/database/**/*.rb
* lib/gitlab/dependency_linker/**/*.rb
* lib/gitlab/diff/**/*.rb
* lib/gitlab/downtime_check/**/*.rb
* lib/gitlab/email/**/*.rb
* lib/gitlab/etag_caching/**/*.rb

Partially addresses gitlab-org/gitlab-ce#47424.

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 replaces the repository param.
This allows more flexiblity as sometimes we have highlight content
not related to repository. Sometimes we know ahead of time the language
of the content. Lastly language determination seems better fit as a
logic in the Blob class.
`repository` param is only used to determine the language, which seems
to be the responsiblity of Blob.

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".

These are clear wins.

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

Previously, this wasn't needed: text was normally set to the highlighted
contents anyway. Now, it is: we store different things in text and rich_text.

This caused https://gitlab.com/gitlab-com/production/issues/439.

Previously, this wasn't needed: text was normally set to the highlighted
contents anyway. Now, it is: we store different things in text and rich_text.

This caused https://gitlab.com/gitlab-com/production/issues/439.

This assures that old cache is not used if we change format of
cached data.

If a file is deleted, its new_pos is 0 (less than
total_blob_lines), but there is no reason to add the
bottom 'match' line in this case because there is not
extra content which could be expanded.

This currently causes 500's errors when loading the MR page
(Discussion) in a few scenarios.

We were not considering detailed diff headers such as
"--- a/doc/update/mysql_to_postgresql.md\n+++ b/doc/update/mysql_to_postgresql.md"
to crop the diff. In order to address it, we're now using
Gitlab::Diff::Parser, clean the diffs and builds Gitlab::Diff::Line objects
we can iterate and filter on.

We request Gitaly in a N+1 manner to build discussion diffs. Once the diffs are from different revisions, it's hard to make a single request to the service in order to build the whole response.
With this change we solve this problem and simplify a lot fetching this piece of info.

Today, when fetching diffs of a note, we always go to Gitaly in order to diff between commits and return the diff of each discussion note. With this change we avoid doing that for notes on the "current version" of the MR.

This adds a method to track errors that can be recovered from in
sentry.

It is useful when debugging performance issues, or exceptions that are
hard to reproduce.

Port of "Fix XSS on commit diff view" for 10-6

See merge request gitlab/gitlabhq!2364

These can be a `BatchLoader` which is proxying a nil, while not being concrete
nils themselves.

This may lead to some being evicted and having to be cached again, but many MRs
get closed or updated in that time anyway.

Previously, we kept them all in the cache. We don't need the highlight results
for older diffs - if someone does view that (which is rare), we can do the
highlighting on the fly.

Rugged sometimes chops a context line in between bytes, resulting in the context
line having an invalid encoding: https://github.com/libgit2/rugged/issues/716

When that happens, we will try to detect the encoding for the diff, and
sometimes we'll get it wrong. If that difference in encoding results in a
difference in string lengths between the diff and the underlying blobs, we'd
fail to highlight any inline diffs, and return a 500 status to the user.

As we're using the underlying blobs, the encoding is 'correct' anyway, so if the
string range is invalid, we can just discard the inline diff highlighting. We
still report to Sentry to ensure that we can investigate further in future.