feat: add forward+ rendering

destrum/assets_src/shaders/mesh.vert

@@ -10,6 +10,10 @@ layout (location = 2) out vec3 outNormal;
 layout (location = 3) out vec4 outTangent;
 layout (location = 4) out mat3 outTBN;
 
+// The depth pre-pass reuses this shader, positions have to match bit for bit
+// so the main pass can depth test against it with LESS_OR_EQUAL
+invariant gl_Position;
+
 void main()
 {
     Vertex v = pcs.vertexBuffer.vertices[gl_VertexIndex];