Allow ActorScrollers to use SetDrawByZPosition without turning off Loop

Previously, if I wanted to do SetDrawByZPosition(true) on an ActorScroller, I would also have to SetLoop(false).  This prevented me from actually looping ActorScrollers that were z-positioned.

There is already a metric for this (LoopScroller) which I can set to true without having it impact SetDrawByZPosition.  This commit should not impact the _fallback or default themes as neither use SetDrawByZPosition anywhere.

Feedback from someone who knows more about this is definitely encouraged.