Reimplemented GtkExtendedLayout on GtkBin

Reimplemented GtkExtendedLayout on GtkBin

Instead of implementing ->get_desired_size() on GtkBin, which
cant really be done because border widths are in the domain of
the concrete subclasses; here we implement only the get_height_for_width
and get_width_for_height apis - GtkBin subclasses whom might have a
variable border width depending on allocations need to write their
own height-for-width implementations.