Test with multiple browsers at once

I'd like to test my scenarios with Firefox, Chromium AND webkit. Right now, it looks like I'll have to make or script three individual runs to achieve that.
Would it be possible to pass an array here, thus tripling the number of tests?

```
engine: "playwright",
engineOptions: {
browser: ["chromium", "firefox", "webkit"],
},
```

Start at the Playwright engine and the engineOptions.browser configuration entry point. Trace how a single browser is selected and how scenarios are scheduled, then verify that passing chromium, firefox, and webkit runs each scenario in all three browsers.

Written by the indexing model from the issue text.