[Feature Request] New InstancedStaticMeshComponent API: Add Multiple Instances

Licensee says that adding multiple InstancedStaticMeshComponent instances can be very slow (main bottleneck being the physics building).

I think there's a good case for a method something like:

    void AddInstances(const TArray<FTransform>& InstanceTransforms, TArray<int32>* OutOptionalIndices);

or

    TArray<int32> AddInstances(const TArray<FTransform>& InstanceTransforms, bool bReturnIndices);

which adds multiple instances at once (preferably even in parallel), and performs physics building asynchronously, in a similar manner to ProceduralMeshComponent.