HDRenderLoop: Add k_identity4x4

Assets/ScriptableRenderLoop/ShaderLibrary/Common.hlsl

                                 0.0, 1.0, 0.0,
                                 0.0, 0.0, 1.0};
 
+const float4x4 k_identity4x4 = {1.0, 0.0, 0.0, 0.0,
                                 0.0, 1.0, 0.0, 0.0,
                                 0.0, 0.0, 1.0, 0.0,
                                 0.0, 0.0, 0.0, 1.0 };