VLCMediaPlayer: Allow to get time/position from any thread
requested to merge umxprime/VLCKit:umxprime/media-player/observe-time-updates-from-any-thread/001 into master
Previous implementation forced user to get time and position from the main thread and configured the time update loop asynchronously.
These changes are configuring the time update observing loop synchronously and are allowing to get time and position with proper concurrent access.