Output property that has to be set to the number of visible instances in the batch after culling.
Note: Setting it to -1 will render all instances in the batch disregarding the data in BatchCullingContext.visibleIndices. As a quick optimization, if all the instances in a batch end up being visible after the culling, it's best to set visibleCount property to -1 to avoid the indirection of rendering using visibleIndices.