Add stj bultin

[newmasterSG]

Fixes #9367

Context

System.Text.Json and System.Memory should be implicit build in roslyntaskfactory

Changes Made

-- Add runtime (Core or Framework) checker for test Doc
-- Add to default namespace STJ and Memory, when app runs by net core
-- Add ITestoutput for roslynTaskFactory tests

Testing

-- Problem with building test, because netstandart does not include STJ and Memory assemblies

Notes

Runtime version naming could change for .net core. Sometimes that's can be as Core, but for new version that's DotNet

[rainersigwald]

I would not expect these references to be required. Are they?

[rainersigwald]

This adds the default namespaces, but I think you'll also need to add a reference to the "common assembly references" section below.

[campersau]

What about System.Text.Json.Nodes? I guess I could manually add the namespace myself, just wanted to ask because I would use it :)

[newmasterSG]

I tried but that didn't worked, as I understood because need to their .dll files located in folder dotnet/ref which is standard folder for getting these assemblies

[newmasterSG]

I can create a new special folder where their dll can be located, however I wouldn't prefer this way

[rainersigwald]

That shouldn't be necessary--you should be able to use the copies MSBuild itself will use at runtime as references (ideally we'd pass a ref assembly to the compiler as that's all it needs, but I wouldn't want to increase the size of MSBuild just to support these references).