[wip] Navigate the frames of a stacktrace.

While a trace is active, allow navigation up and down the call stack with a `NavigationView` that attaches to the bottom of the workspace.

- [ ] Create a panel view and attach it to the bottom of the workspace.
- [ ] Show the name of the active stacktrace. If there is no active stacktrace, hide the view, but don't destroy it.
- [ ] Navigate back to the `StacktraceView`.
- [ ] Allow the stacktrace to be deactivated.
  - [ ] Remove the activation controls from the `StacktraceView`, it makes more sense here.
- [ ] Navigate to the next and previous frames.
- [ ] Notices if you manually navigate to a different frame, within the same editor or a new one.
- [ ] Navigate to the last active frame if you open other editors.