Add pooling for mania barlines

[smoogipoo]

At COE, it was brought up to me that this map wasn't loading: https://osu.ppy.sh/beatmapsets/501530#mania/1073952 Turns out that it is loading, just very slowly.

The primary reason is that it creates some 200k drawables, which this PR directly addresses. The implementation here is similar to the taiko one.

The second reason, which is not addressed in this PR, and likely doesn't need to be addressed, appears to be some inefficiency in HitObjectContainer resulting in what looks to be worst case sort complexity:

i.e. every object added to the HOC causes the HOC to immediately be re-sorted:

osu/osu.Game/Rulesets/UI/HitObjectContainer.cs

Lines 153 to 164 in 01eceea

	private void bindStartTime(DrawableHitObject hitObject)
	{
	var bindable = hitObject.StartTimeBindable.GetBoundCopy();
	bindable.BindValueChanged(_ =>
	{
	if (LoadState >= LoadState.Ready)
	SortInternal();
	});
	startTimeMap[hitObject] = bindable;
	}