wrapper for eigen(Matrix A) where A is hermitian by value but not type

[johnfgibson]

A small fix to make the generic eigen work for matrices that are hermitian by value but not by type, following @dlfivefifty's suggestion at https://discourse.julialang.org/t/eigen-not-working-for-arbitrary-precision-bigfloat/67686/11

[andreasnoack]

For reference, the current error is

julia> eigen(big.(A + A'))
ERROR: MethodError: no method matching eigen!(::Matrix{BigFloat}; permute=true, scale=true, sortby=LinearAlgebra.eigsortby)
Closest candidates are:
  eigen!(::StridedMatrix{T}; permute, scale, sortby) where T<:Union{Float32, Float64} at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/eigen.jl:148
  eigen!(::StridedMatrix{T}; permute, scale, sortby) where T<:Union{ComplexF32, ComplexF64} at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/eigen.jl:171
  eigen!(::StridedMatrix{T}, ::StridedMatrix{T}; sortby) where T<:Union{Float32, Float64} at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/eigen.jl:427 got unsupported keyword arguments "permute", "scale"
  ...
Stacktrace:
 [1] eigen(A::Matrix{BigFloat}; permute::Bool, scale::Bool, sortby::typeof(LinearAlgebra.eigsortby))
   @ LinearAlgebra /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/eigen.jl:237
 [2] eigen(A::Matrix{BigFloat})
   @ LinearAlgebra /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.6/LinearAlgebra/src/eigen.jl:235
 [3] top-level scope
   @ REPL[3]:1

It would probably be more appropriate to adjust the eigen! methods in this package such that they have the same keyword arguments as the ones in LinearAlgebra.

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.21 :warning:

Comparison is base (2f2f4e6) 82.59% compared to head (6e17f92) 82.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
- Coverage   82.59%   82.38%   -0.21%     
==========================================
  Files          11       11              
  Lines        1637     1641       +4     
==========================================
  Hits         1352     1352              
- Misses        285      289       +4     

Impacted Files	Coverage Δ
src/eigenSelfAdjoint.jl	92.23% <0.00%> (-0.86%)	:arrow_down:

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