No need for a proper library, this is just a common location to simplify
JNI bindings in other projects like filamat and gltfio.
There is no need to move the one Java source file (`NioUtils.java`)
since downstream libraries will have a dependency on Filament, and
FindClass should work fine.
This replaces the previous "curvature to roughness" method. Both are related
and rely on the screen space variance of geometric normals but this new
solution offers more control (the screen space variance and the clamping
threshold can be controlled).