Microsoft.AspNetCore.App.Ref 3.1.8 doesn't contain System.IO.Pipelines.xml: missing API docs

[dagood]

Describe the bug

https://www.nuget.org/packages/Microsoft.AspNetCore.App.Ref/3.1.8 doesn't contain System.IO.Pipelines.xml, even though it has System.IO.Pipelines.dll. My understanding is this leaves users without documentation when they use System.IO.Pipelines through ASP.NET Core.

https://www.nuget.org/packages/System.IO.Pipelines/4.7.2 does have this doc XML file in it, so this may just be an issue with how the XML files are redistributed by ASP.NET.

There are also a number of other files in the package without matching XML files, but I'm assuming that's the same issue.

@omajid originally reported this at dotnet/source-build#1686, I'm filing this to track an upstream fix. Once it's fixed in an updated targeting pack, we'll uptake in source-build in the same servicing cycle.

To Reproduce

Download the nupkg (zip), open it, look in ref\netcoreapp3.1\. This also shows up when you install the SDK in e.g. C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1:

#> ls 'C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\*.dll' | %{ $_.FullName.Replace('.dll', '.xml')} | ?{ -not (test-path $_) }
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\Microsoft.Win32.Registry.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Diagnostics.EventLog.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.IO.Pipelines.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Security.AccessControl.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Security.Cryptography.Cng.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Security.Cryptography.Xml.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Security.Permissions.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Security.Principal.Windows.xml
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\3.1.8\ref\netcoreapp3.1\System.Windows.Extensions.xml

[wtgodbe]

Resolved by #26146