A redesign of popover was needed: it can no longer query the application state directly due to current state being its own actor, so instead the popover gets a dedicated copy of the relevant state.
I'm not entirely happy with the extra complexity of having an extra actor just for 1 string, but at least the duplication between C and Rust and mutual calls have been reduced.
This will help make the init procedure safer, by limiting the number of Rust objects that need to be carried to the C side and may be mangled on the way there.
The second benefit is that it allows outputs to become part of new state management.
This ensures that the new state machine is fed events, as well as that its results are applied.
The old ad-hoc system is removed.
There is one regression where the last layout will be used when the panel is brought up manually.
