Switch from PlaySignalAdapter to message bus sync handler

[jdm]

I started doing this conversion and then discovered something that I'm not sure how to handle:

media/backends/gstreamer/player.rs

Lines 752 to 755 in 5bc0391

	let error_handler_id = inner.player.connect_error(move |player, error| {
	notify!(sender_clone, Err(PlayerError::Backend(error.to_string())));
	player.stop();
	});

This error handler id is then used here:

media/backends/gstreamer/player.rs

Line 763 in 5bc0391

glib::signal::signal_handler_disconnect(&inner.lock().unwrap().player, error_handler_id);

Is there any equivalent construct possible? Do I still need to use the PlaySignalAdapter just for this particular case, @sdroege?