The current object can be thought of as the this object that the
builder is working for and will often be used as the default object
when an object is optional.
[method@Gtk.Widget.init_template] for example will set the current
object to the widget the template is inited for. For functions like
[ctor@Gtk.Builder.new_from_resource], the current object will be %NULL.
Sets the current object for the @builder.
The current object can be thought of as the this object that the builder is working for and will often be used as the default object when an object is optional.
[method@Gtk.Widget.init_template] for example will set the current object to the widget the template is inited for. For functions like [ctor@Gtk.Builder.new_from_resource], the current object will be %NULL.