Implement the brush, suspicious sand and suspicious gravel

[MEMOxiiii]

Implements the brush, suspicious sand, and suspicious gravel.

About the item that comes out of a suspicious block: in vanilla the loot comes from
the loot table of the structure the block generated in. A suspicious block you place
yourself is empty and gives you nothing when you brush it, which is how it works in
the game as well. Dragonfly doesn't generate structures and has no loot tables, so
for now nothing comes out. The Item field on the block is where that item goes, so
if structure generation is added later it only needs to be filled in and the
brushing already works.

I added tests for the brushing stages, the item dropping, the progress resetting and
a suspicious block breaking when it falls.

[MEMOxiiii]

ready for review