effects/private: Move highlight inside thumbnail component
..so that they always match in size, regardless of different combinations of drag&drop and animation states.
And also fix selected property to use id-qualified access.
effects/desktopgrid: Restore position correctly when dropping a window
This required a bit of a magic on the WindowHeap side to store and restore global position of a WindowHeapDelegates' window thumbnails.
An additional property bool animationEnabled on a delegate level enables the heap to restore position without playing unneeded initial animation, just like the heap itself.
Windows that are being dragged or already returning form a drop are positioned higher than others on a z-stack.