create-svelte: allow importing JSON modules

[GrygrFlzr]

Since Vite supports directly importing JSON modules this should be enabled in tsconfig.json so that TypeScript or VS Code doesn't complain about it.

This doesn't need to be added to jsconfig.json.

[dummdidumm]

Question is, if we want that option or a declare module "*.json"; in global.d.ts. Adding the tsconfig flag means JSON files will get scanned by TS to infer the type structure, which is very handy but can also be very slow for large JSON files. What's the 80% use case here?

[GrygrFlzr]

Oh, interesting. Considering this is a Vite feature I thought Vite might have already added that type definition, but it seems to be missing from vite/client.d.ts.

Does the flag make TS scan all JSON files, or only imported ones? It seems to make sense to me that if you're explicitly importing a JSON file that you probably want to manipulate it in some way instead of treating it as a black box, so the type information would be useful compared to just getting Record<string, any>. You're right about the size though, stuff like lists of countries which was the use case that prompted this PR can be quite large.

This raises the question if it should be enabled for jsconfig.json or not. It doesn't complain, but it also doesn't show any type information if the flag isn't enabled. I guess we don't enable jsCheck anyway, so maybe we're assuming people are picking JS to opt out of types?

[dummdidumm]

It only will scan the imported ones. Where the breaking point for large JSON files is, I don't know - but I guess we are talking megabytes here, not kilobytes. We had an issue over at language-tools once where intellisense was getting really slow because of it.

[dummdidumm]

Let's just roll with it and maybe act once the sufficient people report slowness in the IDE