Add a new method that tells the surface whether to accomodate
exclusive zones set by other surfaces or not.
right until now this was possible by setting the eclusive zone of
this surface to the value of -1.
Besides being a magic number, it makes impossible for this surface to
set an exclusive zone by itself if we want to ignore other exclusive zones
This can be used to disambiguate the exclusive edge when the anchors are
on a corner (so there would be 2 candidates)
it's quite quick and dirty mostly to understand if we do want to push
for something along the lines
