Do not generate a default export for files containing only snippets#15843

### Describe the problem After the export of snippets was allowed, it became common practice to use .svelte files only to export snippets, containing only the snippets, the module script and optionally the style tag Even though it does not contain any code related to the file's component, its default export is still generated, which is not only useless code but also pollutes the module's typing ```ts import * as everything from './snippets.svelte' const { default: comp, ...snippets } = everything // Now the typing of snippets is { whatever: () => ReturnType<import("svelte").Snippet> } ``` ### Describe the proposed solution Do not generate a default export for files containing only snippets ### Importance nice to have