Introduce AnyCellConfigurable protocol

[mbaranowski]

@luketomlinson here is an idea from my own experiment along these lines:

You could introduce a new protocol that CellConfigurable inherits from like this:

protocol AnyCellConfigurable {
   func configure(with viewModel: CellViewModelType) // can also be just Any
}
protocol CellConfigurable: AnyCellConfigurable {
    associatedtype ViewModelType: CellViewModelType
    func configure(with viewModel: ViewModelType)
}
extension CellConfigurable {
    func configure(with viewModel: CellViewModelType) {
        // this will crash only in the same case that InstrumentViewController. configureCell reaches the default case with the fatalError
        configure(with: viewModel as! ViewModelType) 
}

Assuming that your tableView is configured to dequeue only cells of type AnyCellConfigurable, you can then replace configureCell(_ cell: UITableViewCell, cellViewModel: CellViewModelType) with just a call like cell.configure(with: viewModel) and they should be functionally equivalent with less boiler plate in the second case.

[mbaranowski]

This idea is implemented in #2