fix: tsconfig includes should cover svelte.config.js

[eltigerchino]

closes #11731

While investigating #11731 , I found that the ambient types from adapters weren't showing up when I tried installing the cloudflare, vercel, and node adapters in a fresh project and tried to access the autocomplete on event.platform.

This PR includes the svelte.config.js file in the generated tsconfig so that when the svelte.config.js file imports the adapter, the ambient types are included for the whole project.

We previously did this in #11886 but had to revert it in #11908 because it was a breaking change.

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[benmccann]

I made this change earlier and then it got reverted in #11908. It's a grey area since it's both a bug fix and breaking change. We should do it in SvelteKit 3 at the very least