Inconsistency: Structure voids can be targeted when not holding their item

Relates to MC-48672. May be a feature request.

21w13a adds light blocks, which are intended to be invisible and not obstructive. They have the added mechanic that they can only be targeted when a light block item itself is in the hand, stopping them from getting in the way of other blocks while still giving them a large hitbox to make them not too difficult to destroy or manipulate. Barrier blocks and structure voids are also intended to be invisible, however their hitboxes always appear regardless of the item in the player's hand. It is therefore completely impossible to target past a barrier (potentially intended), and structure voids use a tiny hitbox (MC-221848) to allow them to be targeted past, which makes targeting them themselves challenging.