Structure Configured Features to Structures

Since there is now the "step" property in structure files, maybe configured features that are structures should transfer to structures.

For an example of a structure configured feature to a structure:

{
  "type": "minecraft:jigsaw",
  "biomes": "#minecraft:is_overworld",
  "step": "underground_structures",
  "spawn_overrides": {},
  "start_pool": "minecraft:monster_room/base",
  "size": 1,
  "start_height": {
    "type": "minecraft:uniform",
    "min_inclusive": {
      "absolute": 0
    },
    "max_inclusive": {
      "absolute": 0
    }
  },
  "use_expansion_hack": false
}