Add ManagedMediaSource support for iOS compatibility

[forderud]

Follow instructions on https://developer.apple.com/videos/play/wwdc2023/10122/ (15min into the movie) for how to add ManagedMediaSource support in JavaScript for iOS compatibility.

Subtasks:

• [x] Create ManagedMediaSource instead of MediaSource if available (called on mac)
• [ ] Implement source.onstartstreaming = async () => {...} event handler (never called)
• [ ] Implement source.onendstreaming = async () => {...} event handler (never called)

It's possible to test with Safari on Mac to ease testing.

Links

• W3C spec: ManagedMediaSource
• https://bitmovin.com/blog/managed-media-source/