VSCode test explorer integration

[SteveDesmond-ca]

As a VSCode user, I want to run my tests from within the app, so that I don't need to context switch between the terminal.

Acceptance criteria:

• unit tests can run from within VSCode's test explorer

Probable prerequisite: #51

[Emeka-Ugbanu-hub]

I would love to help with this

[SteveDesmond-ca]

Dug into this quite a bit last night and this morning, and it really doesn't seem feasible to make this fully-featured, given that the core runner expects tests to be already transpiled to JS. Given the number of possible permutations of ways to build tests, I think the best we can do at this point is to list the already-compiled tests and be able to run them from the Testing tab.