.NET Framework SDK container images now contain the Visual Studio 2019 toolset

# .NET Framework SDK container images now contain the Visual Studio 2019 toolset
.NET Framework SDK container images now include Visual Studio 2019 tools. For most scenarios, this change will not be observable, however, there may be some breaks that will be documented in this issue. We did not add additional tools to the SDK, but updated existing tools to match the same tools in Visual Studio 2019. Previously, the tools in SDK matched the same tools in Visual Studio 2017.

We will only produce .NET Framework SDK images that include Visual Studio 2019 tools. We will not produce another set of .NET Framework SDK images that includes Visual Studio 2017 tools. There is a strong goal that the tools remain compatible over releases.

## Discussion
Please share your thoughts on this change and see what others are saying at:

* [Microsoft/dotnet-framework-docker#269](https://github.com/Microsoft/dotnet-framework-docker/issues/269)

## Details
Visual Studio 2019 was released on April 2, 2019. We updated the .NET Framework SDK container images, on the same day, to include a new version of the .NET Framework SDK that contains tools that match the same tools in Visual Studio 2019.

These tools include:
* MSBuild
* NuGet
* C# compiler
* F# compiler
* VB compiler
* VS Test

If you encounter a breaking change or other issues and need to quickly unblock yourself, you can reference the previous version of the image by using its full version tag (e.g. mcr.microsoft.com/dotnet/framework/sdk:4.7.2-20190312-windowsservercore-ltsc2019).

Related pull request: [#252](https://github.com/Microsoft/dotnet-framework-docker/pull/252)

Start with the announcement and review the related pull request #252, then read the linked discussion in Microsoft/dotnet-framework-docker#269. Check the documented Visual Studio 2019 toolset changes and any reported breaks; completion criteria are not defined in this issue.

Written by the indexing model from the issue text.