Different App.PageData for each layout.svelte

[JohnKiller]

Describe the problem

It would be nice if I could set App.PageData different for each layout, and then the pages inside the layout should be forced to extend that interface.

For example, a website may have a "general" layout and an "administrator" layout. I want to set the title on the layout based on the current page data. But inside the admin portal, it is different.

Describe the proposed solution

Have a way to declare the interface inside layout.svelte instead of app.d.ts

Alternatives considered

No response

Importance

nice to have

Additional Information

Related to #11779 because if I can't enforce it, it's not very useful.