Add cop to make sure we don't use ivar in a module

See merge request gitlab-org/gitlab-ce!12800

* upstream/master: (671 commits)
  Make rubocop happy
  Use guard clause
  Improve language
  Prettify
  Use temp branch
  Pass info about who started the job and which job triggered it
  Docs: add indexes for monitoring and performance monitoring
  clearer-documentation-on-inline-diffs
  Add docs for commit diff discussion in merge requests
  sorting for tags api
  Clear BatchLoader after each spec to prevent holding onto records longer than necessary
  Include project in BatchLoader key to prevent returning blobs for the wrong project
  moved lfs_blob_ids method into ExtractsPath module
  Converted JS modules into exported modules
  spec fixes
  Bump gitlab-shell version to 5.10.3
  Clear caches before updating MR diffs
  Use new Ruby version 2.4 in GitLab QA images
  moved lfs blob fetch from extractspath file
  Update GitLab QA dependencies
  ...

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```

Signed-off-by: Rémy Coutable <remy@rymai.me>

Add js prefix for issuable-edit

Closes #40965

See merge request gitlab-org/gitlab-ce!15813

And use .rubocop.yml to exclude paths we don't care,
rather than using the cop itself to exclude.