Automatically add PrivateAssets="All"

[clairernovotny]

I haven't tried this yet in my Extras, but I'm about to --

Rather than having people remember to add PrivateAssets="all" to the PackageReference, if the targets has this:
https://github.com/dotnet/sdk/blob/master/src/Tasks/Microsoft.NET.Build.Tasks/build/Microsoft.NET.Sdk.DefaultItems.props#L53-L56

It can update the metadata automatically. There's no reason a user shouldn't have that for this package... ?

[clairernovotny]

This works for me upon testing it :)

[clairernovotny]

Hmm.... works for me for single target packages but fails for multi targeted ones. Haven't looked closer to see if there's a workaround.

[clairernovotny]

I've filed this too NuGet/Home#6317

[AArnott]

Please post if this ends up working for multi-targeted projects.