Add netstandard configuration for System.Security.Cryptography.Pkcs.Tests

[ViktorHofer]

Currently we don't test the netstandard implementation but only netcoreapp and netfx. For https://github.com/dotnet/corefx/issues/25083 we should add it.

I tried it myself but as some failure popped up I reverted my changes and created this issue.

[filipnavara]

Out of curiosity, do you still have the code that resulted in failure? I have some pending patches for that library and I may take up on this issue as well.

[ViktorHofer]

That's pretty easy to reproduce. Remove the netfx configuration and replace it with netstandard in Configurations.props and in the test.csproj and then run the tests dotnet msbuild /t:RebuildAndTest /p:TargetGroup=netfx.

[ViktorHofer]

Related https://github.com/dotnet/corefx/issues/30728

[bartonjs]

@ViktorHofer It looks like since this was opened we added, then removed, a netstandard configuration in Configurations.props. We're still in the state that we don't have a way to test the netstandard libs in this package, though.

Is there anything that we should still do here?

[ViktorHofer]

The netcoreapp and netstandard(2.1) configurations seem to be identical, still we should test both of them. We could try to enable the tests on UAP which would pick the netstandard one.