Bring `rake postgresql_md5_hash` to CE

Closes gitlab-ee#6419

See merge request gitlab-org/gitlab-ce!19830

[Rails5] Fix snippets_finder arel queries

Closes #47832

See merge request gitlab-org/gitlab-ce!19796

Backport EE .flayignore lines to CE

See merge request gitlab-org/gitlab-ce!19829

Deny repository disk access in development and test

See merge request gitlab-org/gitlab-ce!19716

Fix flakey time-sensitive user comment on issue test

See merge request gitlab-org/gitlab-ce!19786

Fix fields for author & assignee in MR API docs

Closes #42445

See merge request gitlab-org/gitlab-ce!19798

Remove incorrect CI doc re: PowerShell

Closes #40164

See merge request gitlab-org/gitlab-ce!19622

Bring changes from EE for lib/system_check/simple_executor.rb

See merge request gitlab-org/gitlab-ce!19782

Invalidate cache with project details when repository is updated

Closes #33733

See merge request gitlab-org/gitlab-ce!19774

Add assignee lists to tiers table in docs

See merge request gitlab-org/gitlab-ce!19756

Fix shoulda-matchers in Rails 5

Closes #47639

See merge request gitlab-org/gitlab-ce!19749

Wrap YAML error in Web IDE pipelines panel

Closes #47755

See merge request gitlab-org/gitlab-ce!19736

enable CommonMark as the default

See merge request gitlab-org/gitlab-ce!19331

Fixed six broken links in README.md

See merge request gitlab-org/gitlab-ce!19797

Rails5 ActionController::ParameterMissing: param is missing or the value is…

Closes #47805

See merge request gitlab-org/gitlab-ce!19763

Rails5 fix no implicit conversion of Hash into String

Closes #47835

See merge request gitlab-org/gitlab-ce!19792

Rails5 fix stack level too deep

Closes #47804

See merge request gitlab-org/gitlab-ce!19762

Closes #42445.

Closes #40164.

There is a bug https://github.com/rails/arel/issues/531 in Rails 5.0 and
5.1 in Arel/ActiveRecord.

This commit converts arel based queries to their raw counterparts to
make the finder work in Rails 5.0.

These changes should be reverted when on Rails 5.2 as since that version
such queries work well again. See the bug link.

Fix branch name encoding for dropdown on issue page

Closes #47472

See merge request gitlab-org/gitlab-ce!19634

Remove the btn-xs class from the stylesheets

Closes #46743

See merge request gitlab-org/gitlab-ce!19719

Rails5 fix no implicit conversion of Hash into String. ActionController::Parameters no longer returns an hash in Rails 5

Resolve "Merge request diff loading icon not visible"

Closes #47830 and #47849

See merge request gitlab-org/gitlab-ce!19758

Remove card class from the git-empty containers

Closes #47847

See merge request gitlab-org/gitlab-ce!19785

Bring changes from EE for parallel_importer.rb

See merge request gitlab-org/gitlab-ce!19779

Flex board columns

See merge request gitlab-org/gitlab-ce!19250