Floating islands buffet generation replaces stone with end stone

Bug description:

When generating a floating islands buffet world (any biome), all stone and underground resources are replaced by end stone. This issue has only occurred as of the 20w21a snapshot.

Reproduce:

To reproduce this bug, simply generate a buffet world using the floating islands world type and select any biome while playing on snapshots 20w21a or 20w22a.