The old item pointers (which aren't safe to keep around) were
removed in favour of opaque references (void*) which are then
compared against existing items when needed.
Also improves brightening by brightening the whole footprint
(ie: its pads, drawings, reference and value) rather than just
its target cross.
(cherry picked from commit 30e90b0)
For some DRC checks, the location of the marker is not the location
of the first item in the resulting DRC_ITEM, so centering the screen
on PointA of the DRC_ITEM can be confusing.
