Adds a Secret Area Tile Type to Super Metroid.

These tiles are not revealed by any means other than Samus moving into one, at which point the entire section of tiles will break very quickly, revealing a hidden area.

Secret Area Tiles can have solid edges, which change into another solid block when broken instead of air, letting you create new level data around the revealed Secret Area.

The tiles that solid edges change into are stored in a table in Bank $8A, and pointed to by the X-Ray Graphics Room Pointer.

Secret Areas can be fully built automatically in SMILE RF version 3.1.25 by right-clicking in the Level Editor and selecting Edit Secret Areas.