Add guidance for unit test debugging in VS Code

[bleroy]

We currently have topics on getting started with unit testing using xUnit and MS Test, but those topics don't explain how to debug tests. Doing so with Visual Studio is not particularly hard, so could be explained succinctly, but a VS Code version would also be needed, and would probably need to be a little more detailed.

@mairaw

[bleroy]

Related: #1772

[mairaw]

@gregvanl do you guys have any topics on the vs code docs that cover debugging unit tests that we could link to? Thanks!

[gregvanl]

@mairaw We don't have anything in our main code.visualstudio.com docs but there is an example for an Angular TypeScript project in our recipes repo https://github.com/weinand/vscode-recipes/tree/master/Angular-CLI#debug-unit-tests
For .NET, the best place to look might be the C# extension README and repo at https://marketplace.visualstudio.com/items?itemName=ms-vscode.csharp and https://github.com/OmniSharp/omnisharp-vscode

[IEvangelist]

Already covered elsewhere