Load Convertibles from datapack

[Cheaterpaul]

Convertibles can now be registered through datapacks. Registering convertibles over the api is still supported, but will always be overridden by datapack changes.

All json files in data/<modid>/vampirism/convertibles are loaded.The entity id is resolved by foldername:filename.

E.g the file data/<modid>/vampirism/convertibles/minecraft/fox.json defines the minecraft:fox entity as convertible.

{
  "handler": {
    "type": "vampirism:special",
    "converted_type": "vampirism:converted_fox"
  },
  "overlay": "vampirism:textures/entity/vanilla/fox_overlay.png"
}

The handler and overlay fields are optional. If no handler is specified it uses the vampirism:default handler. In case of no overlay, no overlay will be rendered.

Available converting handler are:

• vampirism:default -> adds dummy entity that copies all entity data from the source entity
• vampirism:special -> replaces entity with the given converted_type

By default some attributes are increased when converting an entity. These are knockback_resistance, max_health, attack_damage and movement_speed.

They can be manually configured

{
  "handler": {
    "type": "vampirism:special",
    "attribute_helper": [
      {
        "attribute": "minecraft:generic.knockback_resistance",
        "fallback_base": 0.0,
        "modifier": 1.3
      },
      {
        "attribute": "minecraft:generic.max_health",
        "modifier": 1.5
      },
      {
        "attribute": "minecraft:generic.attack_damage",
        "modifier": 1.3
      },
      {
        "attribute": "minecraft:generic.movement_speed",
        "modifier": 1.2
      }
    ],
    "converted_type": "vampirism:converted_fox"
  },
  "overlay": "vampirism:textures/entity/vanilla/fox_overlay.png"
}

[maxanier]

I'm more in favor of "never change a running system", but this is nice to have, if it is properly tested and documented.