Storybook (dev server): refresh CEM when a component is updated

[florian-sanders-cc]

Fixes #989

What does this PR do?

• Improve the viteFinal config handling. We rely on the mergeConfig helper from vite to avoid erasing parts of the builder config by mistake. This is on par with the Storybook docs (see viteFinal - Storybook).
• Add vite to our dev dependencies. We need to for the mergeConfig helper (although we could rely on the storybook node modules one) + the types. Note that since v8.0.0, storybook automatically adds vite to the dev dependencies so this feels like the right move anyway?
• Regenerate CEM everytime a component is updated (in dev mode only). (see #989 for more info + the comments within the code to review).

How to review?

• Check both commits (the first commit's diff is not easy to read, you might as well just check the code itself for the config at least),
• Run storybook locally, go to a component's doc page and update the doc of the component you are viewing. The doc story should reload and you should see the modified doc.
• The "built" version (preview/prod) should not be affected by these changes so nothing to check expect that the preview has been built and is working.

[Galimede]

Note: if you modify a .d.ts type file, it wont trigger cem again. Still, if you wanted to then modify the doc of the related component after modifying the .d.ts, in hope that it would do the trick and reload cem, the type displayed will remain the same as before.

[florian-sanders-cc]

Note: if you modify a .d.ts type file, it wont trigger cem again. Still, if you wanted to then modify the doc of the related component after modifying the .d.ts, in hope that it would do the trick and reload cem, the type displayed will remain the same as before.

As discussed in sync, this issue was already present with older storybook version. The d.ts files are not actually seen as modules by the dev server so even if it detects a change, it does not trigger any refresh. I've tried to solve it with the same logic as the one used within this PR but this didn't workout: the fact that these files are not recognized as dependencies of other files is the main issue.

I'll open an issue to see what we can do in the future but I'll merge this PR as is in the meantime.

Thanks @Galimede for pointing this out and testing with me :sunglasses:

[github-actions[bot]]

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