Implement VS Test Explorer integration tests

[Youssef1313]

Currently, our integration tests are command-line based. I think it may be worth having integration tests for VS.

[Evangelink]

They are doable but pretty complex to achieve. We were so far relying on TE tests to say whether MSTest is fine or not but given the reported bugs it seems this is not reliable.

@drognanar would you be able to point us to the tests and maybe some doc so we could replicate some?

[Youssef1313]

There are some integration tests for VS on Roslyn side which we can have inspiration from as well https://github.com/dotnet/roslyn/tree/main/src/VisualStudio/IntegrationTest/New.IntegrationTests

But yeah would be good to have more examples, maybe more simplified than roslyn, from @drognanar