Parallel Jacobi symmetric eigendecomposition.

Reference implementation taking from XLA's eigh_expander which is built on the approach in: Brent, R. P., & Luk, F. T. (1985). The solution of singular-value and symmetric eigenvalue problems on multiprocessor arrays. SIAM Journal on Computing, 6(1), 69-84. https://doi.org/10.1137/0906007