Core: Replace cpy with fs-extra copy/copyFile

[strmer15]

Issue: #15174

What I did

Replaces the cpy library used by @storybook/core-server with the previously-installed fs-extra library. The cpy function was copying two things: the favicon and the contents of prebuiltDir.

For copying the favicon, I used the copyFile function, which needs to have the full paths of both the source and destination file, so I changed the destination to append the basename of the favicon to the output directory.

For copying the prebuiltDir, the copy function in fs-extra will copy the contents of a directory into another directory recursively, which seems like is exactly what cpy was doing before. The only difference that I could see between the old use of cpy and fs-extra was that fast-glob follows symlinks by default whereas fs-extra only seems to do so when dereference is true, so I added that option. (fast-glob is used by globby which is used by cpy)

How to test

• yarn test completes successfully
• yarn build-storybook in the examples/cra-ts directory works correctly

Unfortunately, I couldn't figure out how to get the prebuildDir to show up - I added some logging to see if it ever got triggered, but none of the examples seemed to exercise it. I'm not sure how to enable that option to verify that it's working and would appreciate some help!

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

If your answer is yes to any of these, please make sure to include it in your PR.

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[ndelangen]

I've done something very similar in my 7.0 future branch! 👍 Thank you for this @strmer15 👏

[strmer15]

I've done something very similar in my 7.0 future branch! 👍 Thank you for this @strmer15 👏

No problem! Thanks for reviewing @ndelangen !

[ndelangen]

Congrats on your first merged PR to storybook! 🎉