Improve MSBuild SDK resolver by parsing global.json with System.Runtime.Serialization.Json

[jeffkl]

This is a proposed replacement of #2879. This PR uses a built-in class to read global.json so we still get validation of the file's schema but we don't need to load Newtonsoft.Json and other assemblies.

The perf gain isn't as great as using a Regex but it does reduce the resolve time from ~288ms to 100ms.

Bug

Addresses: dotnet/msbuild#4025
Regression: No

• Last working version:
• How are we preventing it in future:

Fix

Details: Use the built-in System.Runtime.Serialization.Json.JsonReaderWriterFactory to read global.json instead of Newtonsoft.Json. The built-in libraries are always NGen'd/CrossGen'd and will load faster.

I also cleaned up the unit tests to use NuGet's built in test utility instead of the one we added when the SDK resolver was copied here from the MSBuild repo

Testing/Validation

Tests Added: Yes
Reason for not adding tests:
Validation:

[zivkan]

I think the PR title is wrong. It's using System.Runtime.Serialization.Json, not System.Xml. The Json APIs might use types from System.Xml, but we're not using XML APIs to read the JSON file.

[zivkan]

Given NuGet is already targeting .NET Core 3.1 and later, is there a benefit to using System.Text.Json's JsonReader instead?

[jeffkl]

For .NET Framework, we'd need to ship a separate assembly which I don't think would JIT as fast. The size of global.json is very small and so the performance gain mainly comes from not having to load a big DLL to read it. So I think System.Text.Json would probably not be a good candidate for this. Ideally we'd use some native library to read it so its even faster.

[jeffkl]

I think the PR title is wrong. It's using System.Runtime.Serialization.Json, not System.Xml. The Json APIs might use types from System.Xml, but we're not using XML APIs to read the JSON file.

Its definitely confusing. I'm using JsonReaderWriterFactory which returns an XmlJsonReader that implements an XmlReader from System.Xml. You end up calling the same methods as if you're reading an XML file while under the covers its reading it as JSON. So I titled this with "reading JSON via System.Xml". I'm more than happy to rename it

[jeffkl]

@zivkan and @nkolev92 please review at your earliest convenience

[nkolev92]

LGTM

[nkolev92]

🔪