An error pops up when adding reference to Winforms .net core application

_From @Marie-Shi on January 17, 2019 9:26_

**OS:** RS4 x64
**VS:** 16.0.0 Preview 3.0 [28516.179.d16.0stg]
**.NET SDK:** .NET Core 3.0.100-preview-010110

**More info:** This issue cannot repro on Console and Class library .net core applications.

**Steps to Reproduce:**

1. Install .NET Core 3.0 SDK available from https://github.com/dotnet/core-sdk.
2. Create a Winforms .Net Core application by command: dotnet new winforms –o “xxx”.
3. Open the project and right click ‘Dependencies’ to choose ‘Add Reference’.
4. Click ‘Browser’ button to choose *.dll(e.g.: System.Windows.Forms.dll) from C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\3.0.0-preview-27315-14, then click ‘OK’ button.

**Actual:**
An error pops up. Please see the below screenshot:
Exception log:
[Add_Reference_CallStack.txt](https://github.com/dotnet/winforms/files/2767980/Add_Reference_CallStack.txt)

**Expected:**
System.Windows.Forms.dll can be added successfully.

_Copied from original issue: dotnet/winforms#330_