This is simpler than having to proxy the action (and target) for the button.
Previously the button was created on demand, but now that we always create it (and hide it when not required), we might as well have users set action and target directly on the button instance.
Minor downside is that labels for open and closed files are no longer aligned.
It would be nice to find a solution for that, but without dropping the stack view, as it saves us > 100 lines of code.
