Add support for the vscode testing API. This would allow for auto-discovering and running t/*.t tests tests directly in vscode. Open to design decisions, but I suspect we should run them via https://perldoc.perl.org/TAP::Harness as it is a core module and we can leverage the perl interpreter setting (as opposed to requiring a user to specify a location for the prove binary).

This is what the API looks like for an example set of tests in Python.

https://code.visualstudio.com/api/extension-guides/testing