The original intention of `get_build` was as a workaround not to violate
`CodeReuse/ActiveRecord`. `find_by_id` does the exact same thing but
does not violate the rubocop rule.

Inside of `Projects::ArtifactsController` and
`Projects::BuildArtifactsController` we fetching the build by id using
active record directly which violates `CodeReuse/ActiveRecord` rubocop
rule. Create `get_build` inside of `project` model which does the same
thing.

`project.latest_successful_builds_for(ref)` is being used to find a
single job all the time. This results into us having to call `find_by`
inside of the controller which violates our CodeReuse/ActiveRecord
rubocop rule.

Refactor `project.latest_successful_builds_for(ref)` to
`project.latest_successful_build_for(job_name, ref)` which will execute
the `find_by` inside of the model.

Also create `project.latest_successful_build_for!(job_name, ref)` which
raises an exception instead of returning nil.

This reverts commit c48e7dc2633f8ee8f38150b050938f43e75bd207.

# Conflicts:
#	app/controllers/projects/artifacts_controller.rb

This makes to always proxy reports

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.

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

Since Rails 5 request.format gets set by extension if it's not explicitly
set.
That means artifacts_controller#file no longer works as expected.
This commit explicitly sets request.format for artifacts_controller#file.