Directory view is kind of stinky

[NattyNarwhal]

Stinky for lack of a better word. I'm rolling my own NSBrowser-like construct, but it has weird issues:

• Double-click handler (onTapGesture) seems swallow normal single clicks a lot. It's weird.
  • The album view item works around this by installing its own NSGestureRecognizer, but this seems really awkward to do without an NSHostingView hoisting the whole thing.
• Keyboard isn't handled for drill-down/deselect on left/right arrows; I think we can use focus bindings plus onKeyPress, but that latter API shows up in 14.

I'm tempted to just wrap NSBrowser or a modern replacement (i.e. this one) in NSViewRepresentable because I'd just be rolling my own version of miller columns in SwiftUI, but worse.