https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26248 added
support for deduplicating FindCommit requests using Gitaly ref name
caching. However, not all endpoints were covered, and in one case the
Gitaly wrapper wasn't actually surrounding the serialization step. We
can safely cache ref names between FindCommit calls for #index and #show
endpoints for merge requests and pipelines. This can significantly
reduce the number of FindCommit requests.

This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points

When we unhooked ClustersController from
Project::ApplicationsController, we missed an EE override to
handle_not_found_or_authorized.

Rather than carry on with override RoutingActions, make a specific proc
for Project that we override in EE instead. Use that proc in both
Clusters::BaseController and Project::ApplicationsController.

Enables frozen string for some vestigial files as
well as the following:

* app/controllers/projects/**/*.rb
* app/controllers/sherlock/**/*.rb
* app/controllers/snippets/**/*.rb
* app/controllers/users/**/*.rb

Partially addresses #47424.

Closes #49120

This commits replaces `params` with `safe_params` in `url_for` helpers
to resolve security issues [1] and failing specs with the

```
ArgumentError:
  Attempting to generate a URL from non-sanitized request parameters!
  An attacker can inject malicious data into the generated URL, such as
  changing the host. Whitelist and sanitize passed parameters to be secure.
```

error.

[1]: https://gitlab.com/gitlab-org/gitlab-ce/issues/45168

So we can distinguish between the permissions on the source and the
target project.

- `create_merge_request_from` indicates a user can create a merge
  request with the project as a source_project
- `create_merge_request_in` indicates a user can create a merge
  request with the project as a target_project

This prevents creating merge requests targeting archived projects.

This could happen when a project was already forked, but then the
source was archived.