Add transpose/adjoint specializations for block Bidiagonal

[jishnub]

With this, the adjoint of a block Bidiagonal will also be a Bidiagonal, following the behavior of a Diagonal.

julia> m = rand(Int8, 2, 2)
2×2 Matrix{Int8}:
 -50  -123
 -11    18

julia> B = Bidiagonal(fill(m,4), fill(m,3), :U)
4×4 Bidiagonal{Matrix{Int8}, Vector{Matrix{Int8}}}:
 [-50 -123; -11 18]  [-50 -123; -11 18]  …      ⋅     
     ⋅               [-50 -123; -11 18]         ⋅     
     ⋅                   ⋅                  [-50 -123; -11 18]
     ⋅                   ⋅                  [-50 -123; -11 18]

julia> B'
4×4 Bidiagonal{Adjoint{Int8, Matrix{Int8}}, Vector{Adjoint{Int8, Matrix{Int8}}}}:
 [-50 -11; -123 18]        ⋅             …        ⋅       
 [-50 -11; -123 18]  [-50 -11; -123 18]           ⋅       
       ⋅             [-50 -11; -123 18]           ⋅       
       ⋅                   ⋅                [-50 -11; -123 18]

julia> B''
4×4 Bidiagonal{Matrix{Int8}, Vector{Matrix{Int8}}}:
 [-50 -123; -11 18]  [-50 -123; -11 18]  …      ⋅     
     ⋅               [-50 -123; -11 18]         ⋅     
     ⋅                   ⋅                  [-50 -123; -11 18]
     ⋅                   ⋅                  [-50 -123; -11 18]

[dkarrasch]

If we do this, than we can remove methods a la

/(A::AbstractMatrix, B::Transpose{<:Any,<:Bidiagonal}) = A / copy(B)
/(A::AbstractMatrix, B::Adjoint{<:Any,<:Bidiagonal}) = A / copy(B)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.05%. Comparing base (e53b50c) to head (c82e846).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1231      +/-   ##
==========================================
+ Coverage   92.03%   92.05%   +0.02%     
==========================================
  Files          34       34              
  Lines       15459    15443      -16     
==========================================
- Hits        14227    14216      -11     
+ Misses       1232     1227       -5     

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