Support `test_driver.set_permission()` inside `.any.js` (for workers)

test_driver is only designed to work on the window context. Which is fine as many webdriver commands like moving pointers only makes sense there, but set_permission is often required also for workers to enable certain features there, e.g. service worker-specific showNotification() behind notification permission.

Perhaps we can:

• Provide some way to tunnel the test_driver requests to the main thread as service_worker_test() does?
• Or provide a way to run a script on the main window before starting the tests in the worker context?

Start with the test_driver.set_permission() entry point and the .any.js worker context, then compare how service_worker_test() handles requests. Determine how permission setup should work before worker tests run, and consider both tunneling requests to the main thread and running a main-window script. Done means workers can use set_permission() for features such as service-worker showNotification().