[2.0] Re-implement `InteractionBarView`

[Sjmarf]

This should tie into the Action system I implemented in #999. However, not all interaction bar widgets can be represented with actions - the info stack and upvote/downvote counters, for example. Therefore, we'll need some sort of enum to represent widgets, which InteractionBarView could accept an array of. Something roughly like this:

enum InteractionBarWidget {
    case scoreCount(any Interactable1Providing)
    case upvoteCount(any Interactable1Providing)
    case downvoteCount(any Interactable1Providing)
    case infoStack([InfoStackWidget]) // InfoStackWidget is an unimplemented enum
    case action(any Action)
}

If we didn't want to use any Interactable1Providing as arguments of the enum directly, we could instead accept a Counter struct which would be defined roughly like so:

struct Counter {
    let value: Int
    let leadingAction: (any Action)?
    let trailingAction: (any Action)?
}

With InteractionBarWidget looking something like:

enum InteractionBarWidget {
    case infoStack([InfoStackWidget])
    case counter(Counter)
    case action(any Action)
}

Models could be responsible for creating their own Counter objects in computed properties called scoreCounter etc, in the same way that they instantiate their own Action objects.