[docs] update vite-plugin-svelte issue status

[bluwy]

Based on sveltejs/vite-plugin-svelte#114, it was closed because I think we should rely on an external svelte preprocessor to handle the asset hashes in the template, as there aren't any advantage having it built into vite-plugin-svelte. Plus the preprocessor can be used for other bundlers as well.

ps: the preprocessor linked is shamelessly the one i built

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