[MC-164535] /playsound uses wrong feedback message for multiple targets

The bug

The /playsound command should use different feedback messages depending on whether one or multiple players are targeted:

commands.playsound.success.single
commands.playsound.success.multiple

However, currently the code always uses commands.playsound.success.single:

net.minecraft.server.commands.PlaySoundCommand#playSound

if (collection.size() == 1) {
    cn2.sendSuccess(new TranslatableComponent("commands.playsound.success.single", sj2, collection.iterator().next().getDisplayName()), true);
} else {
    cn2.sendSuccess(new TranslatableComponent("commands.playsound.success.single", sj2, collection.iterator().next().getDisplayName()), true);
}