[MCPE-155321] Custom structures do not properly generate Jigsaw blocks

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": {}
    }
  }
}