Metatiles can be given a name. The name becomes a constant in
includes/contstants/metatile_labels.h.
The plan is to be able to reference metatiles in code using a macro
like `METATILE(Building, TV_ON, Primary)`, which will evaluate to the
value 0x003, or `METATILE(BrendansMaysHouse, MOVING_BOX_OPEN, Secondary)`,
which will evaluate to the value 0x270.