A site decorator that disallows changing the normal. This is useful for
perimeter sites that stay at one point on a figure. Normally connectors
change the normal of a site so that the figure looks better.
This class is often used so that the site that points out of a terminal
can be properly manhattan routed so that it always leave the terminal in
the ight direction.
Set the normal "out" of the site. If the site cannot
change its normal, it can ignore this call, so clients
that care should always check the normal after calling.
If the site can change its normal, it can also change
its position. For example, a site on the perimeter of a
figure may move to a different position.