This does not replace some instances of `setImmediate` in helpers and
test environment configuration files, as these are well-contained, and
can be rewritten later, if need be. The addition of the lint rule should
prevent more usages of `setImmediate` appearing.

This is the final part of
https://gitlab.com/gitlab-org/gitlab/-/issues/344247.

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.

This might need a better docstring update, could also
be done in a nicer way

This is largely a straight-forward copy of the Karma spec, with the
usual Karma->Jest necessary changes.

This also fixes a bug in the implementation that was causing the tests
to fail, when run on Jest/node, whereby actions that return rejected
promises would always fail the given test. This was due to those
rejections not being caught in the same call stack in which they were
created.

Copy missing helpers from Karma to Jest

Sets `updated_at` so that the transformed note is returned together with
the new reply

Closes #44604

Formats dates
Fixes clipboard button
Simplifies HTML