Vite: Fix framework option checks, and SSv6

[IanVS]

Issue:

We used to be able to get a simple react or svelte from options.framework, but no longer. This adds a bit of a helper to check whether the framework is a string or an object, and return the value. It also adjusts the format of the expected returns to be @storybook/react-vite for instance. This should be merged before #19026, which will need to be updated a bit after these changes.

What I did

How to test

• 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.

[shilman]

I think this is duplicative to work that's already been done on the webpack side of the house.

// always returns an object
const frameworkOptions = presets.apply('frameworkOptions');

I'd propose we move this utility into the common preset and we try to move all framework-specific code out of the vite builder. I'm fine with leaving it in now since we're in transition.

Also reactOptions / svelteOptions will be removed in 7.0 & there will be a migration:

export const framework = {
  name: '@storybook/react-vite';
  options: {
    // former reactOptions
  }
}

[IanVS]

Thanks @shilman. I pulled the utility up to core-common and used it in webpack as well. And I fixed the frameworkOptions like you pointed out. Appreciate it!

[shilman]

LGTM!