Svelte Dynamic snippets doesn't work without user interactions

[j3rem1e]

Describe the bug

The source dynamically generated for a svelte story isn't show until the user changes an arg or clicks on another story.

This is caused by this commit 5c1e2b4

In order to support "async loaders", the function prepareForInline is asynchronous. However, the SourceContainer doesn't seem to be able to handle asynchronous source events.

To Reproduce
Steps to reproduce the behavior:

1. In svelte-kitchen-sink, open the Button story
2. Click on the "Doc" tab
3. The preview doesn't have any sources attached
4. Change a property
5. The source is updated but show the previous code (change in 4 is not visible)

Additional context
Storybook v6.2.1, Svelte addon

┆Issue is synchronized with this Asana task by Unito

[j3rem1e]

@shilman I don't know if we should revert the commit or fix the real bug: Today, the doc addon can't handle asynchronous loader.

The injection of args from the url doesn't seem to work either.

[shilman]

@j3rem1e let's revert the async loader support. it doesn't work in other frameworks yet anyways, so we can bring it back later

[shilman]

Jeepers creepers!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.2.2 containing PR #14444 that references this issue. Upgrade today to the @latest NPM tag to try it out!

npx sb upgrade