Reduce mania editor allocations with many objects selected

[EVAST9919]

master	pr

Last big one is caused by .Reverse() in https://github.com/ppy/osu/blob/ef413c08f19a0743a2aa7020aa72047118828adb/osu.Game/Screens/Edit/Compose/Components/Timeline/TimelineBlueprintContainer.cs#L130 since it allocates a new array under the hood. Needs rethinking probably.