commands are editor.action.copyLinesDownAction and editor.action.copyLinesUpAction
Shift + Alt + DownArrow
Windows: Shift+Alt+Down and Shift+Alt+Up
Mac: Shift+Option+Down and Shift+OptionUp
Linux: Ctrl+Shift+Alt+Down and Ctrl+Shift+Alt+Up (Might need to use numpad Down and Up for Linux)
Alt + UpArrow Alt + DownArrow