When sharing a context between tests and using `'on-first-retry'` we
could end up with tracing still running in non-retried tests. That's
extra overhead without a reason.
- Uses some auto fixtures to set default options and instrumentation on BrowserType.
- Moves screenshot, trace and video to worker-scoped fixtures.
- Throws in page/context when used from beforeAll/afterAll.
- Plumbs around BrowserType to be accessible from Browser and BrowserContext.
