Custom structures do not use the target pool to generate the structure and do not get removed in this process.

Steps to Reproduce:
1. Download the example addon below

2. Install it how you would install all other addons (click on it for windows 10)

3. Create a new world

4. Make sure experimental gameplay is turned on. (custom biomes)

5. Activate the behavior pack

6. Finish creating your world

Observed Results:

• Parent structure properly generates
• Jigsaw blocks do not generate the child structure
• Jigsaw blocks do not get replaced by the defined block.

Expected Results:

• Parent structure properly generates.
• Jigsaw blocks generate the targeted pool, if pool is not found it should print an error.
• The Jigsaw block should always be replaced with the defined block. If the defined block is invalid it should print an error, and replace the Jigsaw with air.

Other Notes

• Java Edition's jigsaw blocks have a level slider and a generate button. Having these in Bedrock Edition would be useful for debugging
• Possibly include a field inside the structure_template_feature that tells the game how many levels to generate.

  {    
    "format_version": "1.18",
    "minecraft:structure_template_feature": {
      "description": {
        "identifier": "custom:parent_feature"
      },
      "structure_name": "custom:parent",
      "adjustment_radius": 8,
      "facing_direction": "random",
      "jigsaw_level": 1, // The number of jigsaw blocks to generate, default: 0, all ungenerated jigsaws should get replaced with their defined block
      "constraints": {
        "grounded": {},
        "unburied": {}
      }
    }
  }