Create/Update assets for version 1.19-pre1

data/minecraft/structures/ancient_city/city_center/_list.json

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+{"directories":["walls"],"files":["city_center_1.nbt","city_center_2.nbt","city_center_3.nbt"]}

data/minecraft/structures/ancient_city/city_center/walls/_list.json

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+{"directories":[],"files":["bottom_1.nbt","bottom_2.nbt","bottom_left_corner.nbt","bottom_right_corner.nbt","bottom_right_corner_1.nbt","bottom_right_corner_2.nbt","left.nbt","right.nbt","top.nbt","top_left_corner.nbt","top_right_corner.nbt"]}