Add in a focus-ring type.

[museun]

This should take in a list of ids and an option for whether it should wrap, along with the keybindings for forward and reverse.

This type should allow nesting.
So in the hypothetical following:

let first = ring([a, b, c];
let second = ring([d, e, f];
ring([first, second]);

The focus index starts at a in the first ring and when it reaches c instead of wrapping back to a it'll continue to d. But when it reaches f in the second ring it should wrap back to a in the first ring.

[museun]

This should probably be a navigation ring instead.

We really need to redesign/reclassify what Focus even means.

Originally, Focus was a locked KEY_INPUT kind of filter that only that view got key_events.

But its confusing if/when navigation would be added. I think the EventInterest::FOCUS should be changed to something else that denotes 'first' go at the event (and they can sink it to keep it from going to other views.)

Another obvious issue: How would events traverse between nested rings? Can rings be self referential?

let t = ring([a,b,c])
let u = ring([d,e,f])
ring([t,a,d,u] // what happens here?