Add test project for c# 13 (pre-release version)

[bjornhellander]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 97.61905% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.45%. Comparing base (ff5c432) to head (e239f6c).
Report is 11 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3864   +/-   ##
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  Coverage   97.45%   97.45%           
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  Files         926      931    +5     
  Lines      110237   110279   +42     
  Branches     3315     3315           
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+ Hits       107433   107474   +41     
- Misses       1837     1838    +1     
  Partials      967      967           

[bjornhellander]

@sharwell, I created this mostly to check if there were any regressions so far. None found. Some previous Roslyn problems were fixed and some tests which have syntax errors in them got slightly different behavior, but looks good so far. If you think it is too early to merge this now, I can update this now and then until the time is right.

I added LanguageVersionEx.CSharp13 the way I expect it will be defined eventually even though it was not in place yet.

What do you think?

[sharwell]

Also need to incorporate this to https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/build/build-and-test.yml

[bjornhellander]

Added that one and test.yml to the solution so they are easier to remember :-)