Accept `Objective`s and `Score`s in `scoreboard` commands

[GrantGryczan]

All of these, for example, should be valid for some objective: ObjectiveInstance and some score: Score:

• scoreboard.objectives.add(objective, 'dummy')
• scoreboard.objectives.remove(objective)
• scoreboard.objectives.setdisplay('list', objective)
• scoreboard.players.set(score, 1)
• scoreboard.players.set('a', objective, 1)
• scoreboard.players.add(score, 1)
• scoreboard.players.add('a', objective, 1)
• scoreboard.players.remove(score, 1)
• scoreboard.players.remove('a', objective, 1)
• scoreboard.players.reset(score)
• scoreboard.players.reset('a', objective)
• scoreboard.players.operation(score, '=', score)
• scoreboard.players.operation(score, '=', 'a', objective)
• scoreboard.players.operation(score, '=', 'a', 'b')
• scoreboard.players.operation('a', objective, '=', score)
• scoreboard.players.operation('a', objective, '=', 'a', objective)
• scoreboard.players.operation('a', objective, '=', 'a', 'b')
• scoreboard.players.operation('a', 'b', '=', score)
• scoreboard.players.operation('a', 'b', '=', 'a', objective)