Sets whether this should be mapped along with its parent.
The child visibility can be set for widget before it is added to a container with [method@Gtk.Widget.set_parent], to avoid mapping children unnecessary before immediately unmapping them. However it will be reset to its default state of true when the widget is removed from a container.
Note that changing the child visibility of a widget does not queue a resize on the widget. Most of the time, the size of a widget is computed from all visible children, whether or not they are mapped. If this is not the case, the container can queue a resize itself.
This function is only useful for container implementations and should never be called by an application.
if true, this should be mapped along with its parent.