Reimplement 3D grass similar to other games (th2x, th4)

[DCxDemo]

Currently grass objects are hardcoded into BSP file and toggled via kill/create, this also means every level tdx file stores a copy of all grass layers to be shown (kinda same in th4 though).

Possible solution:

• pre bake various known grass variants from th2x, th4 in separate shared tdx files
• mark bsp materials as grass, store grass height param
• generate extra mesh at runtime, auto detect amout of layers by loading proper tdx file
• grass tdx path can go to level loading struct, if no grass tdx given, can omit grass routines entirely

Texture naming should follow the same convention, like grass<layerNumber_2_digits>.png, this way can swap grass files and keep it compatible. It would also make it as easy as if (GrassEnabled) RenderGrassObjects() without additional scrits on QScript side.