Occlusion Blutility Function to Delete Unseen Static Meshes Actors In Level improving Performance.

Visibility Scan - Tracing on the exterior of the Actor collection.
Actor Collection stored in a Level Layer, thus the Visibility Scan adds Actors hit to a 'Seen' List. When Visibility Scan is completed, we iterate through the Collection List to Find the Actor in the Seen List. If Actor is Not Found add to Unseen List.

1. Use independent Volume to define cubic space to perform scan on 6 sides: front, back, top, bottom, left, right.
2. For each side, perform a incremental line trace in grid pattern from Top-Left to Bottom-Right. Actors hit during the scan are stored in Seen List.
3. Compare Level Layer Actors against Seen List, if Actor is not found, add to Unseen List.
4. Remove Actors in Unseen List.