ScrollingObjectCollection.ManageVisibility takes too long when numerous objects in container

[julienlang]

Describe the bug

Using the MRTK2 ScrollingObjectCollection, when the list of objects in the container is more than just a few (like in the example scenes) the ManageVisibility method, which is called every frame, takes too long and significantly impacts performance: from 60fps to 20fps!

To reproduce

Following instructions in page linked above, create a ScrollingObjectCollection. Add many buttons to its GridObjectCollection. Update the collection.
Using the Unity profiler, you can notice that the Camera pre-render or the LateUpdate (depending on the UseOnPreRender option) takes a lot of time.

Expected behavior

ManageVisibility is not called when the collection hasn't been scrolled.
This is the workaround I have implemented.