Use a copyto! approach in _BandedMatrix(::BandedRows, A), and switch to PermutedDimsArray in bandedrowsdata

[DanielVandH]

This switches from a loop approach over each axis to an approach that instead uses copyto! over each of the diagonal components. Moreover, I switch to PermutedDimsArray instead of permutedims in the bandedrowsdata implementation since permutedims allocates an entire new matrix while PermutedDimsArray is lazy (see, e.g.

julia> A = view(rand(5, 5), 1:2, 1:3)
2×3 view(::Matrix{Float64}, 1:2, 1:3) with eltype Float64:
 0.346535  0.240277  0.96813
 0.888985  0.105294  0.77876

julia> permutedims(A)
3×2 Matrix{Float64}:
 0.346535  0.888985
 0.240277  0.105294
 0.96813   0.77876

julia> PermutedDimsArray(A, (2, 1))
3×2 PermutedDimsArray(view(::Matrix{Float64}, 1:2, 1:3), (2, 1)) with eltype Float64:
 0.346535  0.888985
 0.240277  0.105294
 0.96813   0.77876

)

(I see there are some overloads in src/banded that try and make permutedims lazy for certain types, but for the matrices I was dealing with these overloads were not reaching it. This seemed like a simpler fix for the time being, since I think an alternative requires piracy for my matrices.)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.99%. Comparing base (62e8561) to head (57d63c9).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #488      +/-   ##
==========================================
+ Coverage   89.80%   89.99%   +0.18%     
==========================================
  Files          27       27              
  Lines        3719     3739      +20     
==========================================
+ Hits         3340     3365      +25     
+ Misses        379      374       -5     

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[dlfivefifty]

Should this be copyto!(data_new, A) and then overload _copyto!(::BandedColumns, ::BandedRows, dest, A) with this definition?