Explorer maps sometimes show incorrect colors

On some occasions, explorer maps won’t show correct colors; ocean biomes will show up as land with nonsensical ocean borders.

Steps to Reproduce

1. Create a new world with seed 3. Fly north until you’re at about z -200.

2. Give yourself a Buried Treasure Map using the command ‘/loot give @s loot minecraft:chests/shipwreck_map’.

3. Note how the transition between land and water in the map is overly dithered.

4. Continue traveling north another 400 blocks until you reach the buried treasure.

5. Note how the transition between land and water in the filled out map is nothing like the explorer map.

Source of the Problem

When the explorer map samples biomes, it does so at y0. Cave biomes like Lush and Dripstone caves can generate at this point. To fix this, the height sampled at needs to be moved up.