FIX build-storybook with simplebar esm files

[ndelangen]

Issue: #5788

What I did

I changed a config for webpack for preview

Why

So after a bunch of experimentation and debugging, I found that simplebar & simplebar-react expose .esm.js AND .js AND .min.js files. For the preview configured it so it would load the .js file. Turns out that files doesn't work well within a webpack bundle.

Probably due to multiple polyfills.

I don't really have an explanation for why it worked in dev-mode.

[vercel]

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[codecov]

Codecov Report

Merging #5816 into next will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff          @@
##           next   #5816   +/-   ##
====================================
  Coverage    34%     34%           
====================================
  Files       651     651           
  Lines      9473    9473           
  Branches   1345    1371   +26     
====================================
  Hits       3221    3221           
  Misses     5637    5637           
  Partials    615     615

Impacted Files	Coverage Δ
...b/core/src/server/preview/iframe-webpack.config.js	0% <ø> (ø)	⬆️

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[ndelangen]

It works:
https://5c79992810c59a00079b78bc--storybooks-official.netlify.com/?path=/story/ui-panel--default

[shilman]

@ndelangen Thanks for figuring this out. You're a wizard 🧙‍♂️

[tmeasday]

Hmm.. this seems like a pretty big change no? Could users be relying on us resolving those those fields from package.json?

[ndelangen]

@tmeasday I don't know why it was added, but it was 'recent'.

I added it here:
https://github.com/storybooks/storybook/blob/750831cbc3b0ef59beed6016e49cd5ae9b7b5467/lib/core/src/server/config/webpack.config.iframe.prod.js

But no longer know why..

[tmeasday]

All good then 😆