Explore the VSCode testing API to see if we can use it

[ElianHugh]

Currently we use a task that runs devtools::test_all() for testing, which could be potentially be modified to use the testing API. It could also be used to expand what testing suites are used (e.g. tiny test).

Additional context A solid example of this is with the python extension: https://code.visualstudio.com/docs/python/testing