New code to add structures back to superflat worlds in Bedrock and Java

{ "type": "minecraft:flat", "settings": { "concrete": true, "layers": [ { "block": "minecraft:bedrock", "height": 1 }, { "block": "minecraft:dirt", "height": 2 }, { "block": "minecraft:grass_block", "height": 1 } ], "structure_overrides": [ "minecraft:village", "minecraft:stronghold", "minecraft:mineshaft" ], "biome": "minecraft:plains" } }