This is a port MR for CE

Original MR:

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14141

This commit is the result of running `yarn eslint --fix` after enabling
the `no-implicit-coercion` ESLint rule.  This rule has been added to
our ESLint config here:

https://gitlab.com/gitlab-org/gitlab-eslint-config/merge_requests/14

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

This commit only targets Vanilla JS files.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

* new merge request can be created by sending an email to the specific
email address (similar to creating issues by email)
* for the first iteration, source branch must be specified in the mail
subject, other merge request parameters can not be set yet
* user should enable "Receive notifications about your own activity" in
user settings to receive a notification about created merge request

Part of #32878

Fixes missing dependencies

Setup teaspoon tests for Issuable

This fixes the case when the user wants to add a label. The user has to use the dropdown’s filter input to look for a label and click it in order to see the bug.

Step to reproduce

- Select at least two issues, one label should be present in all issues, other label should be present in at least one.

- On the label dropdown: Deselect label that is present in all issues, look for another issue using the filter input and click it.

- Click on `Update issues`

Before: Unmarked label were kept on selected issues.
Now: Unmarked label is removed from selected issues

expand remaining non-explicit eslint-disable blocks and factor out globals when no-undef encountered

reactivates all tests and writes more tests for it

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

(Also refactored checkChanged slightly.)