Eliminate copies when returning from LAPACK wrappers

[andreasnoack]

Some of the wrapped LAPACK subroutines for eigenproblems support calculation of a subset of the spectrum and return an intereger of the number of eigenvalues calculated. Right now, the wrappers use this integer to return part of the array used by LAPACK. This creates a copy and we might want to avoid that in the LAPACK wrapper and wait until it is strictly necessary, e.g. in exported methods.

[ViralBShah]

I think we are largely ok on this now. Close?

[andreasnoack]

Still an issue in

julia/stdlib/LinearAlgebra/src/lapack.jl

Line 5093 in 2182389

w[1:m[]], Z[:,1:(jobz == 'V' ? m[] : 0)]