Tile map used for sonar scan VFX

The tile map overhaul for the Echoes of Eta underwater start area. Upgraded from the old map that was an OBJ, the underwater map is split into 4x4, each with 4096 resolution to ensure the generated terrain mesh in Unity looks decent, allowing the sonar scan effects to catch even smaller stones.

Since the underwater map is mostly in the dark, the details of the mesh are the highest priority.