Do a live prototype of the basic lightmap functionality baked in to the engine with a specific test scene

Once we have the option of doing balsam --generateLightmapUVChannel to get an attr_uv1 and a lightmap texture size hint in the mesh (in the submeshes), it needs to be proven that the most basic approach (where the lightmap texture is generated by drawing the (sub)mesh with a slightly modified vertex shader, but otherwise normally, targeting the texture) is viable and functional. This is going to be a specific test scene with a single mesh (with one submesh), possibly implemented with custom materials; remains to be seen if possible without engine modifications.