Add tracking events for layout changes of video player

[mathebox]

As the video player can be presented in different layouts, we should trigger tracking events when the layout is changed, as well as adding the current layout to the context (similar to playback speed).

Proposed solution:

• Possible values (currently supported by iOS):
  • inline
  • fullScreen
  • pictureInPicture
  • remote
• Add current_layout to context of tracking events
• Add new tracking VIDEO_CHANGE_LAYOUT
  • Modify context
    • Erase current_layout
    • new_layout for new layout
    • old_layout for old layout