This moves the common camera setup code out of the individual drivers,
and completely removes vup/vright/vpn from the non-software renderers.
This has highlighted the craziness around AngleVectors with it putting
+X forward, -Y right and +Z up. The main issue with this is it requires
a 90 degree pre-rotation about the Z axis to get the camera pointing in
the right direction, and that's for the native sw renderer (vulkan needs
a 90 degree pre-rotation about X, and gl and glsl need to invert an
axis, too), though at least it's just a matrix swizzle and vector
negation. However, it does mean the camera matrices can't be used
directly.
Also rename vpn to vfwd (still abbreviated, but fwd is much clearer in
meaning (to me, at least) than pn (plane normal, I guess, but which
way?)).
I'd been considering it for a while, but in the end, all the issues it
presented made me decide it wasn't worth merging and was never really
worth keeping: it was a neat proof of concept but of little actual use,
especially now everyone either has an OK GPU or would want to stick to
8-bit rendering anyway (sorry L-Havoc).
However, both it and my merge work are preserved in git history :)
I got tired of having to maintain two separate software renderers, but
didn't want to just nuke sw32, so its core changes are merged into sw.
Alias model rendering is broken, but I know exactly what's wrong and how
to fix it, just need to take care due to asm.
