code needs factorization with the main window

Using str*() on a bytestream is a bad idea.

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>

macosx: implemented playback controls for the detached video window (bwd/play/fwd, position, time, fullscreen)

2 things todo:

- get custom artwork for the fullscreen button

- implement window title when using the black ui mode

Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>

Fixes #6261
Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>

close #6252
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>