Replace the gdk_surface_move_to_rect() API with a new GdkSurface
method called gdk_surface_present_popup() taking a new GdkPopupLayout
object describing how they should be laid out on screen.

The layout properties provided are the same as the ones used with
gdk_surface_move_to_rect(), except they are now set up using
GdkPopupLayout.

Calling gdk_surface_present_popup() will either show the popup at the
position described using the popup layout object and a new unconstrained
size, or reposition it accordingly.

In some situations, such as when a popup is set to autohide, presenting
may immediately fail, in case the grab was not granted by the display
server.

After a successful present, the result of the layout can be queried
using the following methods:

 * gdk_surface_get_position() - to get the position relative to its
   parent
 * gdk_surface_get_width() - to get the current width
 * gdk_surface_get_height() - to get the current height
 * gdk_surface_get_rect_anchor() - to get the anchor point on the anchor
   rectangle the popup was effectively positioned against given
   constraints defined by the environment and the layout rules provided
   via GdkPopupLayout.
 * gdk_surface_get_surface_anchor() - the same as the one above but for
   the surface anchor.

A new signal replaces the old "moved-to-rect" one -
"popup-layout-changed". However, it is only intended to be emitted when
the layout changes implicitly by the windowing system, for example if
the monitor resolution changed, or the parent window moved.