[Epic]: NuGet-based MSBuild project SDK resolver improvements

[jeffkl]

Since its original development, the NuGet-based MSBuild project SDK resolver has needed some improvements. Several fixes have been shipped over the years but there are still some issues that we should fix. Other general improvements are also needed.

Open Issues (Query)

• ArgumentNullException leading to a VS crash dotnet/msbuild#7453
• SDK resolvers should have an API to clear state dotnet/msbuild#9164

Fixed in 6.8

• Add event tracing to NuGet.Common and write events for the NuGet-based MSBuid project SDK resolver NuGet.Client#5409
  [Feature]: Add more logging to NuGetSdkResolver #11445

Pull Requests

• Pass SettingsLoadContext to LoadSettingsForSpecificConfigs NuGet.Client#5314
  Lock contention thread pool issues caused by LoadSettings not passing settingsLoadingContext to LoadSettingsForSpecificConfigs #12737
• Simplify MainNodeSdkResolverService dotnet/msbuild#7244
• Add more events to SDK resolution dotnet/msbuild#7390
• Improve NuGetSdkResolver tests NuGet.Client#4367
• Cache global.json in NuGet SDK resolver NuGet.Client#4380
• Lower priority of NuGet-based MSBuild project SDK resolver to run after .NET SDK resolver NuGet.Client#4443
• Use SettingsLoadingContext in NuGetSdkResolver NuGet.Client#4506
• Check for null or empty string for solution path in SDK resolver NuGet.Client#4507
• Properly handle empty solution and project paths in SDK resolver dotnet/sdk#24333