Filler (admin block)

This block is only accessible through cheats. When interacted with, a popup displays a dropdown/search of all blocks, and a "fill" button. When the "fill" button is pressed, the block fills a 1 block high plane out to any barriers nearby with the specified block. This would by useful for world building and creative boulting of large structures. It would save the work of filling the layers to make things solid. You could have a flat surface, build an outline, and fill it with the block.