Fixes:
- a very old bug in depth in DirectRenderer, probably from the original
tfrag stuff. Looked at PCSX2 source code to see how 32/24 bit depths are
handled. This fixes hud sprites being drawn behind level geometry.
- saturate `vftoi4` like the ps2 does when the float is too large,
fixing hidden text in `hud`. For now it's only using this in the font
code because this saturation is actually kinda slow and hasn't been a
problem in other places.
- fix crazy particle spawning issue with blue gun and dripping stuff.
This would happen if particles kill themselves while being processed
(through a callback)