resizing-hbox: set the "actor" property when creating the child meta object
resizing-hbox: set the "actor" property when creating the child meta object

Ensure that the "actor" property is set, so that calls to
clutter_child_meta_get_actor in the child implementation work correctly.

media-explorer/media-explorer,media-explorer/media-explorer,media-explorer/media-explorer,media-explorer/media-explorer