Add client-side PiP support

[teamyayc]

This might be unworkable, but ideally it should be possible to create additional qml elements with webengineviews, and make them float, resize, etc.

This would likely require wrapping video controls as well.

[teamyayc]

possibly use an iframe player instead, so it's easy to crop.

e.g., https://www.w3schools.com/html/tryit.asp?filename=tryhtml_youtubeiframe