Toplevel::windowType becomes a pure virtual function

The method windowType needs actually two implementations:
* one for Clients
* one for Unmanaged

as for Clients also the window rules are checked and hacks are applied
which is both not needed for Unmanaged windows.

To have the Client specific behavior in windowType the function used to
perform two dynamic_casts which made this method one of the most
expensive during compositing, e.g. for ~1000 frames
* called ~43000 times
* ~85000 dynamic casts
* incl. cost of method: 0.24
* self cost of method: 0.05
* incl. cost of the casts: 0.12

After the change to remove the dynamic casts we have for ~1500 frames
in Client::windowType:
* called ~31000 times
* incl. cost of 0.06
* self cost of 0.02

Calls on Unmanaged and Deleted are so low that we do not need to consider
them.

BUG: 306384
FIXED-IN: 4.10
REVIEW: 106349