Migrate to slnx

[martincostello]

Now that Visual Studio 2022 17.4 has been released, all major IDEs should now support .slnx files.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.23%. Comparing base (f56e106) to head (0aa5f5c).
Report is 3 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2623   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files         311      311           
  Lines        7329     7329           
  Branches     1013     1013           
=======================================
  Hits         7053     7053           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.23% <ø> (ø)
macos	96.23% <ø> (ø)
windows	96.22% <ø> (ø)

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