Create a Microsoft.AspNetCore.App.Ref.Internal package

[wtgodbe]

After #21801, we now produce a non-stable targeting pack .msi. This means that in dotnet/installer, they'll need a package from our repo that identifies the non-stable version of the targeting pack. They can't use one of our other nonshipping packages, since those increment with the rest of the repo, while the targeting pack only ships sometimes. The property MicrosoftAspNetCoreAppRefInternalPackageVersion already exists in dotnet/installer as of dotnet/installer#7487, so we just need to create the package.

[wtgodbe]

Fixed by #22372