Display MR unmergeable reasons

For notifying via todo or email.

First, transitions between can_be_merged & cannot_be_merged are removed,
as they are currently blocked in `check_if_can_be_merged`.
`can_be_merge` always returns to `unchecked` first,
before it can transition to `cannot_be_merged` (and vice versa).

We want to avoid repeated notification triggered by repeated transition
between `cannot_be_merged` & `unchecked`.

So we added `cannot_be_merged_recheck` state, similar to `unchecked`,
but as a mean to remember it’s from cannot_be_merged.

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18042/#note_65945407

Since `unchecked` and `cannot_be_merged_recheck` both mean
“we are in the middle of checking if it is mergeable”,
quite often we need to see if merge_status is in either one of them,
so `check_state?` is added to achieve this.

Remove duplicate method

See merge request gitlab-org/gitlab-ce!18886

Allow a user to sign out when on the terms page

Closes #46211

See merge request gitlab-org/gitlab-ce!18875

Resolve "[Rails5] Fix spec/controllers/projects/jobs_controller_spec.rb"

Closes #46227

See merge request gitlab-org/gitlab-ce!18891

Replace the `project/merge_requests/references.feature` spinach test with an rspec analog

See merge request gitlab-org/gitlab-ce!18794

Merge branch 'docs-fixed-typo-microsoft-teams-slug' into 'master'

See merge request gitlab-org/gitlab-ce!18908

Fix: API Documentation typo on Microsoft Teams slug

See merge request gitlab-org/gitlab-ee!5412

Enforce terms acceptance before configuring 2FA

Closes #46256

See merge request gitlab-org/gitlab-ce!18896

Block access to API & git when terms are enforced

Closes #45849

See merge request gitlab-org/gitlab-ce!18816

Vendor Auto DevOps template

See merge request gitlab-org/gitlab-ce!18876

Resolve "Remove modal box confirmation when retrying a pipeline"

Closes #45715

See merge request gitlab-org/gitlab-ce!18879

Remove Gitlab::RepoPath.strip_storage_path

See merge request gitlab-org/gitlab-ce!18904

Allow builds that have been triggered by a user before terms were
enforced access to git. That way the builds can complete as usual.

This prevents a redirect loop when a user has to enable 2FA and accept
the terms.

Now they will need to accept the terms, then enable 2FA, or any other requirements.

This used to be executed because of the post receive worker, but this
uses Gitlab::GlRepository.parse now. So this removes dead code and
reduces the number of calls on `#legacy_storage_path`.

Add 2FA filter to group members page

See merge request gitlab-org/gitlab-ce!18483

Wiki Find Page to opt_out

Closes gitaly#894

See merge request gitlab-org/gitlab-ce!18895

Resolve "[Rails5] Bump Rails5 to 5.0.7"

Closes #46234

See merge request gitlab-org/gitlab-ce!18888

Resolve "[Rails5] Fix `NoMethodError:  undefined method `-' for "3":String`"

Closes #46233

See merge request gitlab-org/gitlab-ce!18892

Resolve "[Rails5] Fix `Route source can't be blank`"

Closes #46228

See merge request gitlab-org/gitlab-ce!18890

Resolve "[Rails5] Fix app/views/groups/issues.html.haml"

Closes #46225

See merge request gitlab-org/gitlab-ce!18889

Support `js-close` as a removal class in UserCallout

See merge request gitlab-org/gitlab-ce!18790

Fixed none merge request files not being openable in the web IDE

See merge request gitlab-org/gitlab-ce!18881

Backport EE specific cluster spec changes to CE

See merge request gitlab-org/gitlab-ce!18866

Add missing tooltip to creation date on container registry overview

Closes #34229

See merge request gitlab-org/gitlab-ce!18767

Remove method call to deprecated method

See merge request gitlab-org/gitlab-ce!18815

Ensure runner_type is updated correctly when assigning shared runner to project

See merge request gitlab-org/gitlab-ce!18874

Resolve "Terms acceptance dropdown menu"

Closes #46210

See merge request gitlab-org/gitlab-ce!18862

Resolve "Move external link icon to end of link instead of front"

Closes #40725

See merge request gitlab-org/gitlab-ce!18828

Closes https://gitlab.com/gitlab-org/gitaly/issues/894

Add documentation for Runner Registration API

Closes #42067

See merge request gitlab-org/gitlab-ce!16484

CE: Helm init before helm repo add

See merge request gitlab-org/gitlab-ce!18882

Given the settings initializer creates Gitaly Storage Settings objects
already, the calls to path can be moved to that initializer.