With a ManagedMediaSource, it can indicate to the JS Player when to start appending content and when to stop. The initial ManagedMediaSource implementation will emit `startstreaming` when there's less than 10s of buffered content ahead of currentTime and will emit `endstreaming` when 30s have been buffered. When we get to 10s left again, `startstreaming` will be refired until 30s more is appended to the ManagedMediaSource
<rdar://problem/106182027>
Pull request: https://github.com/WebKit/WebKit/pull/11060
Committed 261232@main (77fc3174bf28): <https://commits.webkit.org/261232@main> Reviewed commits have been landed. Closing PR #11060 and removing active labels.