HISM causing massive spikes in BuildTreeAsync

Loading a world partition cell containing dense foliage (30k+ instances per cell) causes spikes on lower end hardware of up to 10-15ms and can observe spikes of 2-5ms on high end hardware too primarily in UHierarchicalInstancedStaticMeshComponent::BuildTreeAsync.

In CL#29842740 BuildTreeIfOutdated is updated to run when PrimitiveInstanceDataManager.HasAnyChanges(), which is always the case at runtime when loading a world partition cell, but wasn't the case before this change. If you revert this change the foliage HISM will still render as expected at runtime without the spike caused by rebuilding the cluster tree.

Steps to Reproduce

• Create world partition default level
• Create Foliage Type of any kind
• Paint foliage in one of the corners to cover a good amount of area
• Start PIE or cooked build far enough away that none of the foliage cells are loaded
• Walk towards cells
• Observe spikes in Insights