feat: support experimental doc entries
- Params/options/members are marked as experimental in the docs.
- `experimental.d.ts` is generated that contains all types and
includes experimental features.
- `experimental.d.ts` is references in our tests so that we
can test experimental features.
- `fonts` option is restored as experimental.
This changes PlaywrigtServer to serve connections like `ws://localhost:3333/?browser=chromium`:
- launches the browser;
- talks `browserType.connect`-style protocol over websocket;
- compatible with `connectOptions` fixture.
```js
await playwright.chromium.connect({ wsEndpoint: 'ws://localhost:3333/?browser=chrome' });
```
