macosx: correctly hide the controls within the native fullscreen mode on Lion when displaying a video (closes #5505)

note that the ordinary fullscreen controller panel won't be present atm though

additionally, this commit can potentially impact the layout of the controller zone and lead to ugly effects, so please stress it a bit
(cherry picked from commit 86c4c01c6e17d66dc63dcb321f4ba6acb400fa38)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>