What is needed:

• Add public void bindVisible(Signal<Boolean> visibleSignal) to Element
• Component::bindVisible delegates to getElement().bindVisible(visibleSignal)
• bindVisible has a similar contract as for Element.bindProperty(...):
  • bindVisible(null) unbinds;
  • calling setVisible or a second bindVisible while a binding is active throws BindingActiveException
  • binding is only active while attached;
  • null value behaves as false.
• Memory-optimal feature storage, similar to TextBindingFeature as the visibility has a special handling in the framework;
  • A lightweight VisibilityBindingFeature on the node to hold an optional Registration and Signal<Boolean> reference. Lazily instantiation only when bindVisible is called to avoid overhead for typical components with no bindings.
  • Provide hasBinding(), setBinding(registration, signal), and removeBinding() (disposing registration), similar to TextBindingFeature usage in bindText.
  • Uses ElementEffect.bind() to actually establish a binding.