feat(jest): create jest config package for unit testing (#3678)

* feat(jest): create jest config package for unit testing
* chore: housekeeping
* fix: now we need to explicitly allow importing without extension
* fix: recover EditorDriverInterface import
* Apply suggestions from code review
* chore: yarn

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

js-packages/jest-config/README.md

@@ -0,0 +1,14 @@
+# Jest config for Flarum
+
+This package provides a [Jest](https://jestjs.io/) config object to run unit & integration tests on Flarum extensions.
+
+## Usage
+
+* Install the package: `yarn add --dev flarum-jest-config`
+* Add `"type": "module"` to your `package.json`
+* Add `"test": "yarn node --experimental-vm-modules $(yarn bin jest)"` to your `package.json` scripts
+* Rename `webpack.config.js` to `webpack.config.cjs`
+* Create a `jest.config.cjs` file with the following content:
+```js
+module.exports = require('flarum-jest-config')();
+```