feat: visualize vertex normals as colors by passing normals to fragment shader

shaders/simple.vert

@@ -2,10 +2,13 @@
 
 in layout(location=0) vec3 position;
 in layout(location=1) vec4 aColor;
+in layout(location=2) vec3 aNormal;
 out vec4 vColor;
+out vec3 vNormal;
 layout(location = 0) uniform mat4 transform;
 
 void main() {
     gl_Position = transform * vec4(position, 1.0f);
     vColor = aColor;
+    vNormal = aNormal;
 }