Computes the bounds for this in the coordinate space of
FIXME: Explain what "bounds" are.
If the operation is successful, true is returned. If this has no bounds or
the bounds cannot be expressed in
target's coordinate space (for example if both widgets are in different windows),
false is returned and
bounds is set to the zero rectangle.
It is valid for this and
target to be the same widget.
the `GtkWidget` to query
the rectangle taking the bounds
true if the bounds could be computed