Allow users to enhance the Vue app instance in vue 3

This is a follow up to #125

I will need to add another option: enhancePreviewApp.

Here is how you will use it:

// styleguide.config.js
import { defineConfig } from 'vue-styleguidist'

export default defineConfig({
  enhancePreviewApp: 'styleguide/enhanceApp.js' // path of the file you want to define directives in
})

// styleguide/enhanceApp.js
import directive from '@/directives'
import { defineEnhanceApp } from 'vue-styleguidist'

export default defineEnhanceApp((app) => {
  app.directive('directive', directive)
})

[elevatebart]

@didagu You can skip the function altogether. It was meant to help write the code with the proper types.

It is returning exactly its params without modification.

export default (app) => {
  app.directive('loadable', loadable);
}

[aleksre]

@elevatebart I can’t seem to get this feature to work. It prints out the error:

Module parse failed: Unexpected token (1:14)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
> Copyright (c) silverwind
| All rights reserved.
|

It’s just a normal js file. We already use the renderRootJsx and require options for other files in the same folder and that works as expected, just this one doesn’t work.

The error seems to be linked to actually importing defineEnhanceApp, because it goes away if I remove it without changing anything else and it also comes back if I import defineEnhanceApp from another file (like require.ts) even if I don’t actually use it.