Migrate the navigation Vuex module to a Pinia store

Migrate the Vuex store module in src/store/navigation.js to Pinia with TypeScript, after the related API helpers have been typed, and update all components and tests.

Requires #1138 (closed), #1140 (closed)

At this stage, the calls from elements to navigation/addToScheduledDeletion that were deleted in #1393 (closed) can now be restored.