Present this after having processed the `GdkToplevelLayout` rules.
If the toplevel was previously not showing, it will be showed, otherwise it will change layout according to
GDK may emit the [signal@Gdk.Toplevel:
GdkToplevel:compute-size] signal to let the user of this toplevel compute the preferred size
of the toplevel surface.
Presenting is asynchronous and the specified layout parameters are not guaranteed to be respected.
the `GdkToplevel` to show
the `GdkToplevelLayout` object used to layout