Part 4

Automatic conversion of Vue Test Util `Wrapper#find` for
`Wrapper#findComponent` when applied to a Vue component.

From the Vue Test Util page:
https://v1.test-utils.vuejs.org/api/wrapper/#find

```
Deprecation warning

Using find to search for a Component is deprecated and will be removed.
Use findComponent instead. The find method will continue to work for
finding elements using any valid selector.
```

Convert JSON code blocks into tables
if the code blocks have a table param

Changelog: added

This is helpful at creating a stub for things like GlModal
which technically has public methods in its API

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.

@vue/test-utils 1.x will change behavior for stubs. Now they will
render all available slots instead of defaults. To simplify
migration and taking care of emerging pattern of "stubbing with
props" we're introducing `stubComponent` helper, which will copy
props and model of stubbed component and also ensure that stubbed
component still could be found with default vue-test-utils finders
(this removes several ugly workarounds in our codebase)