Custom world generation/pos rule test

• ： Root tag.
  •  predicate_type: can be the following values: always_true to always pass; linear_pos to pass with a random probability, the probability is based on the 3D Manhattan distance from the current block to the structure start. axis_aligned_linear_pos to pass with a random probability, the probability only based on the distance on the specified axis.

    If predicate_type is linear_pos, the additional parameters are as follows:

  •  min_chance: (optional, default is 0.0) The probability (probability less than 0 is treated as 0, greater than 1 is treated as 1) for the predicate to pass when the distance of a block to the structure start is equal to or less than min_dist.
  •  max_chance: (optional, default is 0.0) The probability (probability less than 0 is treated as 0, greater than 1 is treated as 1) for the predicate to pass when the distance of a block to the structure start is equal to or greater than max_dist. If a block's distance is between min_dist and max_dist, probability is obtained by linear interpolation between the values of min_dist and max_dist, that is, the probability is (distance - min_dist ) / ( max_dist - min_dist ) * ( max_chance - min_chance ) + min_chance, and probability less than 0 is treated as 0, greater than 1 is treated as 1.
  •  min_dist: (optional, defaults to 0) the distance when the minimum probability is used. Must be less than  max_dist.
  •  max_dist: (optional, defaults to 0) the distance when the maximum probability is used. Must be greater than  min_dist.

    If predicate_type is axis_aligned_linear_pos, the additional parameters are as follows:

  •  axis: (optional, defaults to y) can be x, y or z.
  •  min_chance: (optional, default is 0.0) The probability (probability less than 0 is treated as 0, greater than 1 is treated as 1) for the predicate to pass when the distance of a block to the structure start is equal to or less than min_dist.
  •  max_chance: (optional, default is 0.0) The probability (probability less than 0 is treated as 0, greater than 1 is treated as 1) for the predicate to pass when the distance of a block to the structure start is equal to or greater than max_dist. If a block's distance is between min_dist and max_dist, probability is obtained by linear interpolation between the values of min_dist and max_dist, that is, the probability is (distance - min_dist ) / ( max_dist - min_dist ) * ( max_chance - min_chance ) + min_chance, and probability less than 0 is treated as 0, greater than 1 is treated as 1.
  •  min_dist: (optional, defaults to 0) the distance when the minimum probability is used. Must be less than  max_dist.
  •  max_dist: (optional, defaults to 0) the distance when the maximum probability is used. Must be greater than  min_dist.