windowManager: Generalize translation values

windowManager: Generalize translation values

Currently, the translation values are set with the assumption that
one of the actors represents a fullscreen window. In order to
generalize it for any size change transition, we can simply swap
the monitor rect with the source or target rect as appropriate,
and translate the actor from the target to the source position by
subtracting the former and adding the latter.

https://bugzilla.gnome.org/show_bug.cgi?id=766685