add light sample

CMakeLists.txt

liblava-demo/light.cpp

res/light/data.inc

res/light/gbuffer.frag

res/light/gbuffer.fragment.spirv

res/light/gbuffer.vert

res/light/gbuffer.vertex.spirv

res/light/gen_spirv.bat

res/light/gen_spirv.sh

res/light/lighting.frag

res/light/lighting.fragment.spirv

res/light/lighting.vert

res/light/lighting.vertex.spirv

res/light/normal.png

res/light/roughness.png