Gets the preferred height the this would like to be displayed at.
Consumers of this interface can use this to reserve enough space to draw the paintable.
This is a purely informational value and does not in any way limit the values that may be passed to [method@Gdk.Paintable.snapshot].
If the this does not have a preferred height, it returns 0. Negative values are never returned.
the intrinsic height of this or 0 if none.