Add .NET 8 TFM

[hwoodiwiss]

Adds .NET 8 as a supported TFM.
Makes some changes based on API's that have become deprecated with .NET 8.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6cbbd0d) 78.96% compared to head (04ac779) 79.19%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1349      +/-   ##
==========================================
+ Coverage   78.96%   79.19%   +0.23%     
==========================================
  Files         138      138              
  Lines        3232     3230       -2     
  Branches      450      450              
==========================================
+ Hits         2552     2558       +6     
+ Misses        449      441       -8     
  Partials      231      231              

Flag	Coverage Δ
linux	79.19% <100.00%> (+0.23%)	⬆️
macos	47.77% <100.00%> (-0.01%)	⬇️
windows	47.86% <100.00%> (+0.21%)	⬆️

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