feat: add support for svelte.config.ts

[fzn0x]

This added support for svelte.config.ts with minimal changes and independent. This does not provide types support, however, now we could run svelte.config.ts out-of-the-box.

Closes #2576

Note that, svelte.config.js is prioritized by default.

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Latest commit: c5ed56c

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[fzn0x]

Not sure about the others workflow error like playwright can't read or vercel.

[fzn0x]

Looks like it's a flaky tests

[dominikg]

this would create a direct dependency from sveltekit to typescript, forcing everyone, even non-typescript users to install it. That's a big no.

[dummdidumm]

Thanks, but I'm pretty sure this is insufficient. It only transpiles the config file, but as soon as that one imports other TS files you'll get errors.
To support this we would have to bundle/transpile the config on the fly, similar to what Vite does.

[dominikg]

There has not been a consensus that support for svelte.config.ts is going to happen. If it was, it would have to be added at a different level (see discussion in the linked issue) as all tools in the svelte ecosystem would have to be able to read it

[fzn0x]

I will think about other solutions later.

[fzn0x]

Question added in RFC sveltejs/rfcs#59 @dominikg @dummdidumm