Add linalg.lu_solve
This PR adds `linalg.lu_solve`. While doing so, I found a bug in MAGMA
when calling the batched MAGMA backend with trans=True. We work around
that by solving the system solving two triangular systems.
We also update the heuristics for this function, as they were fairly
updated. We found that cuSolver is king, so luckily we do not need to
rely on the buggy backend from magma for this function.
We added tests testing this function left and right. We also added tests
for the different backends. We also activated the tests for AMD, as
those should work as well.
Fixes https://github.com/pytorch/pytorch/issues/61657
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72935
Approved by: https://github.com/IvanYashchuk, https://github.com/mruberry
