More diagnostic improvements

[erri120]

Part of #977 and required for #915.

Changes:

• Replaced Diagnostic.Message with Diagnostic.Summary and Diagnostic.Details.
• Added AddValue<T> to the message builder. This allows you to include any kind of data in the diagnostic message data struct.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 61.53846% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 58.26%. Comparing base (f0b860c) to head (33fb057).
Report is 2 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1004      +/-   ##
==========================================
+ Coverage   58.12%   58.26%   +0.13%     
==========================================
  Files         644      644              
  Lines       21056    21069      +13     
  Branches     1641     1650       +9     
==========================================
+ Hits        12238    12275      +37     
+ Misses       8425     8397      -28     
- Partials      393      397       +4     

Flag	Coverage Δ
Linux	57.52% <61.53%> (+0.08%)	⬆️
Windows	57.40% <61.53%> (+0.11%)	⬆️
clean_environment_tests	58.24% <61.53%> (+0.13%)	⬆️
macOS	56.98% <61.53%> (+0.16%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...sMods.Abstractions.Games.Diagnostics/Diagnostic.cs	66.66% <100.00%> (+4.16%)	⬆️
...ons.Games.Diagnostics/DiagnosticTemplateBuilder.cs	0.00% <ø> (ø)
...ountAndBlade2Bannerlord/Emitters/BuiltInEmitter.cs	57.69% <100.00%> (+0.54%)	⬆️
...Games/NexusMods.Games.StardewValley/Diagnostics.cs	100.00% <100.00%> (ø)
...Tests/Diagnostics/DummyLoadoutDiagnosticEmitter.cs	0.00% <0.00%> (ø)
...del.Tests/Diagnostics/DummyModDiagnosticEmitter.cs	0.00% <0.00%> (ø)
...aModel.Tests/Diagnostics/DiagnosticManagerTests.cs	0.00% <0.00%> (ø)
...cs/DiagnosticTemplateIncrementalSourceGenerator.cs	82.15% <67.74%> (-3.56%)	⬇️

... and 3 files with indirect coverage changes