Fix and use module UseState

[Philipp-M]

This fixes the UseState module to be compilable and usable again with the current xilem architecture.

A port to xilem_core should be straightforward (and could be done in a follow-up PR).

[waywardmonkeys]

Can you add a doc comment here?

[Philipp-M]

If I would understand exactly what UseState does, I'd do ^^ (see zulip thread). I think probably someone else should document the code (maybe in another PR), this function just runs UseState::new obviously, I added the trait bounds, so that it's easier to see in rust-analyzer what is required to get this into a View (as it otherwise doesn't make much sense I think).

[Philipp-M]

Added a comment, could probably be better, but I guess better than nothing for now.

[DJMcNab]

I think we can close this for now. use_state will likely eventually be needed, but we're trying to avoid that for as long as possible...

[Philipp-M]

Yeah lets close this, I don't think we should rely on the app state to be Arc<State> anyway, as this severely restricts the use-cases.
I do hope we find ways to make adapt/map_state/lens more flexible (e.g. modularice distinct state items, as described here), so that we can keep the all the user-state in AppState