Simplify log_det_J of Moebius transformer

[andrrizzi]

This paper uses a very nice trick to compute the log_det_J of the symmetrized Möbius transformer based on the equivariance of the transformation that doesn't require the calculation of the Jacobian matrices. We should check if it makes sense to re-implement the log_det_J of the (standard) Möbius transformation as well using a similar trick to speed it up.