Prior to this commit, if we wanted to compare changes between two
branches in different repositories - for instance, creating an MR from
a fork child to a fork parent - the commits for the fork child end up
in the fork parent's repository. Even if no MR is created, the commits
remain accessible until a garbage collection run is completed.

Since GitLab acts as a SHA oracle, these commits can be found by anyone
with access to the target project, which has a security impact.

Forks are not allowed to be more visible than their parents, but they
are allowed to be less visible, so putting their commits into the fork
parent is a bad idea.

Instead, we can do the comparison in the fork child's repository; the
commit for the target branch can be fetched with the same mechanism we
use for child -> parent fetches at the moment. This prevents disclosure
in the most common case.

This should also have a positive performance impact - a fork child will
already have the commit from the fork parent far more often than the
fork parent, so we'll need to do fetches less often.

Even though this is a security fix, I pulled the code for the affected
method out into a separate class to make the changes clearer. Roughly
the same number of lines are removed or altered; a few more are added,
but I think the increased clarity is worthwhile in this case.

Update timestamp values for software license policies

See merge request gitlab-org/gitlab!23197

Soften warning about spam email to remove mention of service disruption

See merge request gitlab-org/gitlab!23404

Revert short acme order expiration time

See merge request gitlab-org/gitlab!23399

Refactor `spammable_owner_id` method

See merge request gitlab-org/gitlab!23224

Fix POST method in dashboard link for disabling admin mode

See merge request gitlab-org/gitlab!23363

The link for bigger screen sizes has incorrectly GET as method

Fix typo in warning related to Auto DevOps

See merge request gitlab-org/gitlab!23354

Update doc/ci/yaml/README.md

See merge request gitlab-org/gitlab!20233

Cycle Analytics 'Tasks by Type' Chart Filters

See merge request gitlab-org/gitlab!22936

Moves the subject filter into the
new charts filter component and also adds
a label filter

Ensure the menu drops down to the right

Check mergeability of MR asynchronously

See merge request gitlab-org/gitlab!21026

Executing `MergeRequests::MergeabilityCheckService#execute` can be
time consuming and can likely cause a request to timeout.

Moving its execution asynchronously via `#async_execute` will help
in ensuring page and API requests that needs it can load faster.

Add milestone issues display limit

See merge request gitlab-org/gitlab!23102

Fix broken QA test

Closes #197486

See merge request gitlab-org/gitlab!23328

Docs: review previous blame doc

See merge request gitlab-org/gitlab!23357

Add Aggregate Failures block

See merge request gitlab-org/gitlab!23303

Rename whilst to while

See merge request gitlab-org/gitlab!23287

Adds calls_gitaly to the commit type in GraphQL

See merge request gitlab-org/gitlab!23322

Add seed file for container images

See merge request gitlab-org/gitlab!23330

Fix create/delete API calls for approval rules

See merge request gitlab-org/gitlab!23107

Add app validation for any-approver rule uniqueness

See merge request gitlab-org/gitlab!23241

Merge branch '118862-change-dashboard_spec-js-queryselector-based-specs-to-use-find-instead' into 'master'

Use find instead of querySelector in dashboard_spec.js

Closes #118862

See merge request gitlab-org/gitlab!23314

This reverts merge request !22878

Close related issue after error resolve

See merge request gitlab-org/gitlab!22744

This would save us from 500 error raised by database

Expand options for e.g.

See merge request gitlab-org/gitlab!23207

Add version text for new error content

See merge request gitlab-org/gitlab!23386

Add days to completion chart median line to cycle analytics docs

See merge request gitlab-org/gitlab!23062

Edit new content for keys API

Closes #197990

See merge request gitlab-org/gitlab!23384

Add language tags to code blocks

See merge request gitlab-org/gitlab!23208

Code blocks should specify the language the code is in, so we
can enforce a markdownlint rule.

Document CI job activity limit

See merge request gitlab-org/gitlab!23246