This is better be made part of the 2D interface.
That would have been done long ago if it hadn't been for the totally incompatible way this was handled by the purely paletted software renderer.
Now with that out of the way there is no point keeping this code this deeply embedded in the renderer.
Lots of this was still laid out for DirectDraw. This removes most of Begin2D so that it can be done more cleanlz.
Note that this commit renders weapon sprites and screen blends incorrectly. Those will be fixed in an upcoming commit.
With the software renderer not being used for 2D anymore it would be quite annoying if every texture class had to implement these.
If done properly, the SW renderer should actually be forced to dynamic_cast any texture to a FWorldTexture before using this stuff, but that'd be some pointless overhead better saved.
- with renderers freely switchable, some shortcuts in the 3D floor code had to be removed, because now the hardware renderer can get FF_THISINSIDE-flagged 3D floors.
- changed handling of attenuated lights in the legacy renderer to be adjusted when being rendered instead of when being spawned. For the software renderer the light needs to retain its original values.
It may use the same calculations as the hardware renderer but must use the 2D drawer for display.
It should be investigated if the hardware renderer can do this as well.
