The main goal was to get visframe out of mnode_t to make it thread-safe
(each thread can have its own visframe array), but moving the plane info
into mnode_t made for better data access patters when traversing the bsp
tree as the plane is right there with the child indices. Nicely, the
size of mnode_t is the same as before (64 bytes due to alignment), with
4 bytes wasted.
Performance-wise, there seems to be very little difference. Maybe
slightly slower.
The unfortunate thing about the change is the plane distance is negated,
possibly leading to some confusion, particularly since the box and
sphere culling functions were affected. However, this is so point-plane
distance calculations can be done with a single 4d dot product.
While it wasn't the root cause of the disappearing lights (even after
sorting out the light limit issue), because the cause of that was
everything working as designed, I suspect sunlight wasn't reaching as
far as it should. Even it it was, this should be slightly faster
(especially for larger maps) as leafs can be tested 32 or 64 at a time
rather than individually.
Abyss of Pandemonium uses global ambient light a lot, but doesn't
specify it in every map (nothing extracting entities and adding a
reasonable value can't fix). I imagine some further tweaking will be
needed.
The parsing of light data from maps is now in the client library, and
basic light management is in scene. Putting the light loading code into
the Vulkan renderer was a mistake I've wanted to correct for a while.
The client code still needs a bit of cleanup, but the basics are working
nicely.
