Watch mode for testing view

[MKRhere]

Is your feature request related to a problem? Please describe.

The Deno extension has a very nice feature that allows running tests from the VSCode interface. However, this involves manually clicking on "▶ Run Test" each time.

Deno CLI has deno test --watch. It'd be convenient to have that via the extension as well.

Describe the solution you'd like

Add the ability to automatically re-run tests in the sidebar when the test file is saved. It would ideally be next to the "Run tests" button, as a "Run tests and watch" option.