This is both for consistency and better localizability. The old code is retained to ensure that mods inheriting from the old menu continue to work.
# Conflicts:
# src/menu/menudef.cpp
# src/namedef.h
# wadsrc/static/zscript/ui/menu/optionmenu.zs
This was done because the backdrop as implemented was the only texture in the entire game that had to be deleted and recreated each frame.
However, with Vulkan this would have necessitated quite a bit of synchronization with the render pipeline which wasn't really feasible just for this one single texture.
Now the texture manager can assume that once a texture was created it will be immutable and never has to change.
# Conflicts:
# src/CMakeLists.txt
# src/textures/backdroptexture.cpp
# src/v_2ddrawer.cpp
