Eigen/GPU [4/5]: Add sparse solvers, FFT, and SpMV (cuDSS, cuFFT, cuSPARSE)

libeigen/eigen!2414

Closes #3067

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>
Co-authored-by: Rasmus Munk Larsen <rlarsen@nvidia.com>
28 files changed