independent page type

[ignatiusmb]

Closes #3730

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[Rich-Harris]

I guess we'll need to figure out a place to document this. Should it go in https://kit.svelte.dev/docs/modules#$app-stores or do we need to rig up a new section in https://kit.svelte.dev/docs/types?

Also, do we need the export keywords here? If an unexported interface is importable, should it just be const page etc rather than export const page?

[benmccann]

if this is going to close #3730 then I think this interface would need to be exported?

[ignatiusmb]

We already moved all of them to docs/types, so I guess might as well add a new section for the $app/* modules?

Also, do we need the export keywords here?

We don't, surprisingly. They're still importable, it might be how declare module works, but for the sake of consistency, I'll add the export keywords to them.

[Rich-Harris]

In #4099, we're moving Navigation (formerly 'Navigating') to the @sveltejs/kit types, and I think it makes sense to do the same thing here, since these are fairly universal concepts even if they're currently only used inside $app/stores. At the very least it makes documenting things somewhat easier