Generic path in ldiv! for Diagonal

[jishnub]

The performance improvement in ldiv! is best seen using SparseArrays, as this seems to lack a specialized ldiv! method currently:

julia> D = Diagonal(rand(3000));

julia> S = sprand(size(D,1), 0.01);

julia> @btime ldiv!($D, $S);
  29.620 μs (0 allocations: 0 bytes) # master
  15.388 μs (22 allocations: 154.47 KiB) # This PR

This is because the broadcasting method is taken. Unfortunately, in this example, the in-place broadcasting for a sparse array is allocating, but this should be allocation-free in general.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.97%. Comparing base (925acef) to head (548cc05).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1261      +/-   ##
==========================================
- Coverage   92.03%   91.97%   -0.07%     
==========================================
  Files          34       34              
  Lines       15475    15483       +8     
==========================================
- Hits        14243    14241       -2     
- Misses       1232     1242      +10     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.