This reuses the FTexCoordInfo class the hardware renderer had been using to calculate wall texture offsetting.
The software renderers still need this sorted out to bring them in line with the rest of the code, though, but they do not have this code sufficiently well organized to make this a straightforward task.
This was a relic from trying to support ZDoomGL's texture shader system but would make texture management with Vulkan significantly more complicated because it would require dynamic descriptor set management for textures which can cause a lot of overhead.
Decals will now be processed into a list in the processing pass, allowing to use the vertex buffer even on GL3 hardware and to offload this part of the work to a multithreaded worker task.
