GeometryBasics Normal Calculations/general API for specifying normals

[sjkelly]

We have mostly relied on the GeometryTypes API to generate normals. In GB we can do the same, but we shouldn't fix the calls to Mesh. E.g. GLNormalMesh3D should work.

Similarly I have been getting good results using autodiff to make normals on functions, so it would be nice to have an explicit API for passing a normal function to the meshing process.