Move towards geometry instancing for shadows

shader/shadow/light.vert

@@ -0,0 +1,9 @@
+#version 450 core
+layout (location = 0) in vec2 pos;
+layout (location = 1) in vec2 texPos;
+out vec2 vTexPos;
+void main()
+{
+  gl_Position = vec4(pos,0,1);
+  vTexPos = texPos;
+}