Add ElementHandle.isInViewport()

[imiric]

From this discussion in grafana/xk6-browser#467, we wanted to change TestWaitForFrameNavigationWithinDocument to also check whether an element is visible within the viewport after a navigation in the same document happens.

To do that it would be helpful if there was an ElementHandle.isInViewport() method, similar to the one described here. Playwright doesn't have such a method, but Puppeteer has ElementHandle.isIntersectingViewport(). isInViewport seems like a slightly better name, so let's go with that.

Suggested solution

We already have ElementHandle.boundingBox() in Go, though if we want to reduce the amount of JS evaluations and CDP calls, we could just wrap ElementHandle.eval() and do a single CDP call for this.

See #4424 for the test change to use this method.