Player: Rework dispatch_async usage

libvlc_media_player_set_media/stop are now asynchronous.
The usage of dispatch_async is not needed anymore,
except for the libvlc_media_player_release call.
Indeed, this function can be blocking since it can wait for the input closing.
3 jobs for mediaplayer/stop-set/async/01 in 192 minutes and 50 seconds (queued for 62 minutes and 20 seconds)
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passed #466367
macos
continous-MobileVLCKit

03:12:50

passed #466368
macos
continous-TVVLCKit

01:23:59

passed #466369
macos
continous-VLCKit

01:05:40