Add logging throughout the extension

[brettcannon]

And VS Code should have something for this in their March release.

• Ensure errors logged in extension are not (via some config or ability to mock) logged during unit tests
  (else this pollutes the test output and could be confusing).
  Note: Errors are forcibly raised in unit tests.

[brettcannon]

Any place we execute something behind the scenes through a system call we should document, e.g. the command we use to discover tests, to run them, etc.

[brettcannon]

Duplicate of #2156