layout-manager: Add a new animation API

layout-manager: Add a new animation API

It's similar to to the implicit animation API of ClutterActor and
compatible to deprecated API of ClutterBoxLayout and
ClutterTableLayout.

It adds :use-animations, :easing-mode, :easing-duration and
:easing-delay properties to control animations when allocation of a
child has changed. Layout manager implementers should call

use_animations = clutter_layout_manager_get_easing_state (manager,
                                                          &mode,
                                                          &duration,
                                                          &delay);

from the allocate() virtual function to access these values.

https://bugzilla.gnome.org/show_bug.cgi?id=676827