StaffGroup.harp constructor
Factory: Create a harp group (grand staff)
Implementation
factory StaffGroup.harp(Staff trebleStaff, Staff bassStaff) {
return StaffGroup(
staves: [trebleStaff, bassStaff],
bracket: BracketType.brace,
name: 'Harp',
abbreviation: 'Hp.',
);
}