fix: don't bundle @sveltejs/kit

[Rich-Harris]

closes #13894

We've had a long-running battle with instanceof checks inside the codebase: when you call error(...) or redirect(...) in your code, SvelteKit needs to check that the thrown object is an instance of HttpError or Redirect.

Recently we tried #13843, which attempts to ensure that any of your dependencies that depend on @sveltejs/kit are bundled, since @sveltejs/kit is also bundled, and that means that your app will only have a single copy of SvelteKit (and classes like HttpError) in memory. But that has problems of its own.

This PR goes in the opposite direction, by making it possible to not bundle @sveltejs/kit in the first place. Aside from being a lot simpler, this feels more correct. The one compromise is that we need to expose a @sveltejs/kit/internal package so that classes can be shared between code in @sveltejs/kit and code in $app/... (which is bundled, necessarily, as it relies on virtual modules etc). But because we're controlling how types/index.d.ts is generated, this module is invisible to TypeScript (and therefore won't show up in import autocomplete suggestions etc).

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Latest commit: fbf7871

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@sveltejs/kit	Patch

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[elliott-with-the-longest-name-on-github]

Should this not be the package import rather than relative?

[Rich-Harris]

Doesn't really matter as long as you don't use relative imports between bundled and unbundled modules

[elliott-with-the-longest-name-on-github]

Same here

[teemingc]

There's a type checking issue in the Kit package. Since we import from the Kit package namespace, we're also importing the generated types. This causes the '$service-worker' module to be declared twice. Once in types/index.d.ts and again in src/types/ambient.d.ts.

EDIT: actually there's probably another reason since we've already been importing from the Kit package namespace before this without issues

EDIT 2: ok it seems the issue only happens if we import from the Kit package namespace in a unit test file.

[dummdidumm]

I think you can also fix it (and I think that's preferable) to add a path alias for that namespace import (we already have one for the root for the same reason)

[teemingc]

I think you can also fix it (and I think that's preferable) to add a path alias for that namespace import (we already have one for the root for the same reason)

Oh nice. I didn't know you could override packages like that. I've changed it to use the path alias now.