Add classList polyfill for IE classList.toggle('foo', force)

Closes #38916

See merge request gitlab-org/gitlab-ce!15552

Fix pulling and pushing using a personal access token with the sudo scope

Closes #40466

See merge request gitlab-org/gitlab-ce!15571

Update Prometheus Gem version and disable Prometheus method call instrumentation by default.

Closes gitlab-ee#4139 and #40457

See merge request gitlab-org/gitlab-ce!15558

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/38916

[ci skip]

Fix hashed storage for attachments bugs

Closes #40280

See merge request gitlab-org/gitlab-ce!15482

Clean up repository fetch and mirror methods

See merge request gitlab-org/gitlab-ce!15424

Fixed import of render mermaid & render math methods

See merge request gitlab-org/gitlab-ce!15550

Renamed ProtectedBranches::ApiUpdateService to LegacyApiUpdateService

See merge request gitlab-org/gitlab-ce!15575

Simplify the DB changes checklist

See merge request gitlab-org/gitlab-ce!15577

Move identical merged branch check to merged_branch_names

Closes #39887

See merge request gitlab-org/gitlab-ce!15464

Added Rubocop config for background migrations

See merge request gitlab-org/gitlab-ce!15576

Use foreign key to get latest MR diff

Closes #37631

See merge request gitlab-org/gitlab-ce!15126

Fix link text from group context

Closes gitlab-ee#4100

See merge request gitlab-org/gitlab-ce!15565

Allow password authentication to be disabled entirely

Closes #37320

See merge request gitlab-org/gitlab-ce!15223

This removes some somewhat redundant checkboxes from the template and
rephrases the introduction now that those settings are in GDK.

[ci skip]

This adds a Rubocop configuration file specific to
lib/gitlab/background_migrations. This configuration will be used to
(hopefully) make reviewing background migrations easier by enforcing
stricter rules compared to the rest of GitLab. Because this
configuration is directory specific it will only affect background
migrations.

Remove cluster_id from 20171013104327_migrate_gcp_clusters_to_new_clusters_architectures

See merge request gitlab-org/gitlab-ce!15566

Cross link default branch docs to issue closing pattern docs

Closes #40449

See merge request gitlab-org/gitlab-ce!15546

Fix the redirect location wording

Closes gitlab-com/gitlab-docs#142

See merge request gitlab-org/gitlab-ce!15572

Compared to the merge_request_diff association:

1. It's simpler to query. The query uses a foreign key to the
   merge_request_diffs table, so no ordering is necessary.
2. It's faster for preloading. The merge_request_diff association has to load
   every diff for the MRs in the set, then discard all but the most recent for
   each. This association means that Rails can just query for N diffs from N
   MRs.
3. It's more complicated to update. This is a bidirectional foreign key, so we
   need to update two tables when adding a diff record. This also means we need
   to handle this as a special case when importing a GitLab project.

There is some juggling with this association in the merge request model:

* `MergeRequest#latest_merge_request_diff` is _always_ the latest diff.
* `MergeRequest#merge_request_diff` reuses
  `MergeRequest#latest_merge_request_diff` unless:
    * Arguments are passed. These are typically to force-reload the association.
    * It doesn't exist. That means we might be trying to implicitly create a
      diff. This only seems to happen in specs.
    * The association is already loaded. This is important for the reasons
      explained in the comment, which I'll reiterate here: if we a) load a
      non-latest diff, then b) get its `merge_request`, then c) get that MR's
      `merge_request_diff`, we should get the diff we loaded in c), even though
      that's not the latest diff.

Basically, `MergeRequest#merge_request_diff` is the latest diff in most cases,
but not quite all.

Updated all Vue libraries

See merge request gitlab-org/gitlab-ce!15554

Improve environments performance

Closes #32098

See merge request gitlab-org/gitlab-ce!15484

Closes https://gitlab.com/gitlab-com/gitlab-docs/issues/142