fix: use Vite by default for Svelte and Vue

[benmccann]

What I did

New Vue and Svelte projects use Vite by default. Those ecosystems are heavily invested in Vite and promote it as the default builder

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[benmccann]

this should probably change from vue3 to vue if #20970 is merged

[JReinhold]

I'm not sure this will make an actual difference, since we've only ever had three builders, @storybook/builder-webpack4, @storybook/builder-webpack5 and @storybook/builder-vite, so there will always be either webpack or vite in the builder name.

Note that this here is only for the automigrations that runs when users upgrade from v6 to v7, this is not related to the init command at all. That command will pick the builder based on the existence of a Vite config file, implemented here: https://github.com/storybookjs/storybook/blob/next/code/lib/cli/src/detect.ts#L110 was that maybe what you actually wanted to change?

[benmccann]

ah, yes. that was what I wanted to change. thanks for the pointer