VideoPress: Feature request to prevent videos playing when out of viewport

### Summary of request

When a VideoPress video is playing, if a person scrolls down a page the video will continue playing when it is outside of the viewport. On a very long page with a lot of videos, this can make it difficult to identify which video is playing in order to pause it (to begin a new video, for example).

### Suggested solution

An option to allow videos to be auto-paused when not in the viewport.

Requested in this forum thread: https://wordpress.org/support/topic/how-to-pause-video-hosted-on-jetpack-cdn-when-scrolling-out-of-veiwport/

Start by locating the VideoPress video playback component and reviewing the linked forum thread for the requested behavior. Confirm how an option to auto-pause videos outside the viewport should work, including what happens when a viewer scrolls back, then verify the behavior on a page containing multiple videos.

Written by the indexing model from the issue text.