Improve selfhost testing experience #189680
Description
- Make it possible to run extension tests using our running
- This probably entails making a generic VS Code extension test runner (neat!)
- @ulugbekna is passionate about Jest!
- We probably cannot readily copy-paste jest into core tests, but we should see if there's features we miss in Jest that we can bring over
- Any inspiration we can take from the Jest extension to improve UX in core?