refactor(playground): move to ESM module and add type check for config

[fi3ework]

Description

• change all vite config files in the playground to ESM
• add // @ts-check for all config files to be involved in typescheck of playground
• use defineConfig whenever possible to get better type intellisense
• fixed some existing trivial config type errors 😬

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

Thanks for migrating this! 🙏 I suppose this supersedes #8252. I have a few comments below, and ideally we would also need to add "type": "module" to the package.json, but that brings up other minor issues too so it can be tackled later in a separate PR.

[bluwy]

Greatly appreciate the refactors!

[sapphi-red]

Thanks 💚