Accurate papersprite projection

I know there were apparently some crashing issues with the incomplete version of this so pls test for things like that before merging, and also make sure things like scale work right (I'm 87% sure it should but just to be safe)

here is an exe I compiled of this code branch that could be used to test maybe srb2win-accurate-papersprites.exe

I think @toaster wanted to change the position of minecart walls when projection was good but this is targeting master and that would be a [puts on extremely serious voice] Netplay-Breaking Change. so that has to go in separately

changed the description

thousandflags.wad The waving flag swimming pool does no longer crash immediately; been there for 15 minutes and haven't gotten a single crash. I even duped and reduped the object density and all it does is lag, so it seems to work for me so far.

merged

mentioned in commit dc151fc7