Cartesian_to_spherical_coordinates returns NaN gradients near (0, 0, 1).

Hello tensorflow-graphics team,

Could you please update the docstring to mention that NaNs gradients can be returned?
You could also consider printing a warning when the input is close to (0, 0, 1) or returning a gradient other than NaNs (e.g. 1 or 0). Alternatively, branching based on (z/radius) to use arcsin rather than arccos can also minimize numerical instabilities in the gradient, though it may also reduce performance. See [2] for an example.

The docstring mentions that this function is not smooth at (0, 0, 1) but does not specify that NaN gradients can occur. Furthermore, the website [1] is not updated to mention the smoothness and has a dead github link (Related to #383?).

[1] https://www.tensorflow.org/graphics/api_docs/python/tfg/math/math_helpers/cartesian_to_spherical_coordinates
[2] https://colab.research.google.com/drive/1ECn4eYaeQfRfXaC46BX75ZDZmwSkMkWH?usp=sharing

Start with the Cartesian_to_spherical_coordinates entry point and its current docstring, then compare the generated TensorFlow API page linked in the issue. Confirm how the existing text describes smoothness and update the relevant documentation to cover possible NaN gradients and the reported dead link; done means the local and website documentation accurately reflects the function’s behavior.