Release 2.0.0-preview.1

• Esprima: 2.0.2 -> 2.1.2
• System.Text.Json: 5.0.2 -> 6.0.2
• Microsoft.SourceLink.GitHub: 1.0.0 -> 1.1.1
• NUnit3TestAdapter: 4.0.0 -> 4.2.1
• Microsoft.NET.Test.Sdk: 16.10.0 -> 17.0.0
• dropped netcoreapp2.1 testing target
• added net6.0 testing target
• switch build server to windows-2022
• repository cleanup: .gitignore update, copyright years update, remove unused upstream files
• use C# 10
• enable and fix CAxxxx/IDExxxx analyzers
• apply [SkipLocalsInit]
• added readme to nuget
• bumped version to 2.0.0 due to minor public api refactorings:
  • seal classes that not expected to be extended
  • add some missing ArgumentNullException to public APIs
  • DeminifyStackTrace method has additional bool preferSourceMapsSymbols parameter from microsoft/sourcemap-toolkit#86
• fix #16
  • merged microsoft/sourcemap-toolkit#88
  • merged microsoft/sourcemap-toolkit#86
  • add public setters to StackFrame.MethodName and StackFrame.FilePath