Vue 3 does not expose the name of the directive on the binding, so we
must explicitly pass a name to createMockDirective when setting up a
mock.

This is to assist with the slow migration to Vue 3.

It is a bit confusing as we have put helpers to be used in specs in the
same directory as specs for `app/assets/javascripts/helpers`. In oder
to make the destinction a bit more clear, this moves jest test helpers
to `__helpers__` and adds appropriate readmes to both folders.

Part of our prettier migration; changing the arrow-parens style.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34357

**Why?**
- This is helpful at asserting that a specific value
  set on a specific directive of a component.