Inits that are logically singletons (e.g. actor
location or owner) should implement this interface
to avoid runtime inconsistencies.
Duplicate instances are rejected at init-time,
allowing simpler queries when they are used.
This allows callers to efficiently enumerate these returned collections without the allocation and overhead imposed by the IEnumerable interface. All implementations were already returning arrays, so this only required a signature change.
Additionally, internally renamed VisualBounds to SelectionOverlayBounds to avoid confusion with RenderBounds.
This step was necessary to prevent actors with selectable area smaller than their graphics to be removed too early from ScreenMap even though part of the graphics should still be visible.
RA cruisers were a prime example, but to a lesser extent several other actors were affected as well.
This separation also serves as preparation to determine the final RenderBounds from multiple source bounds later, to fix the remaining ScreenMap issues (building 'bibs', aircraft shadows).
Items with no size act unexpectedly as they can fail to be returned when querying partition bins as they do not intersect along the top or left edges of the bin. We prevent such items being added in the first place to avoid this scenario.
As a side effect - we must now prevent any Immobile items that do not have size from being added to the screen map.
