cannot build netstandard2.0 project with the dotnet SDK build

Description

Cannot build as a netstandard2.0 project with the dotnet SDK build.

Repro steps

I have a test project where various SDK versions can be tried.

https://github.com/jackfoxy/TestSqlClient

Known workarounds

Build in Visual Studio 16.3.8 does work.
I have tried Visual Studio 16.4 previews, and they do not build.

Related information

Note in the readme.md file the evolution of error and warning messages produced over the most recent dotnet SDK versions. SDKS prior to 2.1.301 will not even run the build.

```paket install`` gives a warning

Could not detect any platforms from 'typeproviders' in E:\GitRepos\TestSqlClient\packages\FSharp.Data.SqlClient\lib\typeproviders\fsharp41\net461\FSharp.Data.SqlClient.DesignTime.dll', please tell the package authors

related issues

https://github.com/fsprojects/FSharp.Data.SqlClient/issues/318

https://github.com/fsprojects/FSharp.Data.SqlClient/issues/337

https://github.com/fsprojects/FSharp.Data.SqlClient/issues/361

Start with the linked TestSqlClient reproduction and its readme.md, comparing the reported behavior across the referenced dotnet SDK versions. Reproduce the netstandard2.0 build failure and inspect the related FSharp.Data.SqlClient issues for context. Done means the project builds successfully with the dotnet SDK without the reported type-provider warning.