Fix spine::Skeleton not updating on re-entry.

Could be done in a tighter manner by scheduling updates in
spine::SkeletonAnimation instead and listening for animation events.
However, this may need a more robust interface on scheduleUpdate and
unscheduleUpdate to work correctly.
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SpineDrawing fixes
Merge pull request #5489 from ricardoquesada/spine_fixes

SpineDrawing fixes
closed #3684, Set shader program before TextureAtlas is rendered.
closed #3684, Optimize the code of TextureAtlas test case.
issue #4129: EventDispatcher::_listeners -> _listenerMap.
issue #4129: Uses 'const reference' when getting touches by EventTouch::getTouches.
Merge pull request #5490 from natural-law/issue3684

closed #3684: Set shader program before TextureAtlas is rendered.
issue #4129: EventTouch::getTouches return const reference.
closed #4129: Event listeners in engine shouldn't be removed by method removeAllEventListeners().
issue #4129: Remove unused references in Xcode project.
issue #4129: Adds default argument(nullptr) for dispatchCustomEvent.
issue #4129: Adds test case for issue 4119.
Merge pull request #5492 from dumganhar/iss4129-remove-all-listener

closed #4129: Event listeners used in engine shouldn't be removed by method removeAllEventListeners().
Merge pull request #5461 from Wilhansen/spine_skelFix

closed #4156: spine::Skeleton would not be updated after re-adding to scene.
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