this adds the standard menu bar items Services, Hide Others, Show All
and Close, as suggested by Apple's HIG.
https://developer.apple.com/macos/human-interface-guidelines/menus/menu-bar-menus/#app-menu
- Services are useful to add custom actions and shortcuts via the
System Preferences to mpv
- Close is important since the menu bar can open secondary windows, like
About or the Open dialogue. those couldn't be closed with the standard
system shortcut before. this is now possible.