Items in falling vault blocks are invisible

Relates to MC-308628, MC-308629, MC-309011 and MC-309015.

To reproduce: /summon falling_block ~1 ~2 ~2 {BlockState:{Name:"minecraft:vault"},TileEntityData:{config:{"loot_table":"chests/simple_dungeon",key_item:{id:"minecraft:trial_key"}}}}

Expected results: an item would be visible inside of the vault block while it is in a falling state.

Actual results: the item is entirely invisible until the vault becomes a placed block.