Align `schur!` with LinearAlgebra.jl and add `ordschur!`

[albertomercurio]

Hello,

the current implementation of the schur! function is not aligned with the LinearAlgebra.jl one. For example, I cannot get the factorization using F.Z and F.T. Is there a reason behind this?

Also, would it be possible to also add the ordschur! function?

I have noticed that there exists the GenericSchur.jl package that does this. Are you planning to merge its implementation here, as a generic linear algebra package?