Microsoft.Data.SqlClient.SNI not deployed along with WebForms

### Describe the bug
SNI.dll are not in build result (bin) - no x86\SNI.dll, no x64\SNI.dll is present in bin folder after WebForms project build.

### To reproduce
* Create a new web forms project (.NET Framework 4.7.2)
* Create a new class library project with a new CSPROJ format (.NET Framework 4.7.2)
* Add a Microsoft.Data.SqlClient.SNI (version 1.1.1) nuget package reference to the class library project
* Add a class library project reference to the web forms project (web forms will reference the class library)
* (or get the complete solution from https://github.com/jirikanda/Microsoft.Data.SqlClient.SNI-Repro)
* Build the solution

### Expected behavior
The x86\SNI.dll and x64\SNIl.dll are present in a bin folder in class library and in a bin folder of webforms.

### Current behavior
The files are only in class library bin folder.