Add threading analyzers and resolve issues

[pmaytak]

• Add <PackageReference Include="Microsoft.VisualStudio.Threading.Analyzers" Version="17.9.28" PrivateAssets="all" />
• Resolve the issues - fix or suppress.
  • Rules: https://github.com/microsoft/vs-threading/blob/main/doc/analyzers/index.md
• This project doesn't treat warnings as errors. So any default rule severety of warning should be changed to error to match other libraries (IdentityModel). VSTHRD111 (UseConfigureAwait()) rule needs to be set to warning.

[westin-m]

Leaving this in review until PublicApiAnalyzers is enabled in IdWeb to make sure no changes affect the public Api