Make UInstancedStaticMeshComponent::UpdateInstanceBodyTransform protected

From the UDN ticket here: [Link Removed]

We are developing a plug in which contains classes built from UInstancedStaticMeshComponent, overriding its virtual functions to update our mesh instances ourselves. We've hit a snag in that the UpdateInstanceBodyTransform member function used by the ISMC to move instance bodies is currently marked as private - preventing our derived class from using it. Given that UInstancedStaticMeshComponent contains many virtual functions for plug-ins to override in derived classes, we feel that necessary member functions like UpdateInstanceBodyTransform should be marked as protected and not private, allowing derived classes in plug-ins to make use of that member function.

As a short-term solution, we have simply duplicated UpdateInstanceBodyTransform in our derived class, which has proven safe to use. Making the source function protected would remove the need to duplicate the code in our plug-in.