Bad animation_controllers and mob invisible with mobs exported from unmodified templates

[hsivonen]

Steps to reproduce

1. Go to https://mctools.dev/ in latest Firefox on Windows 10
2. Go to the "From a Mob" tab.
3. Create new with Cow.
4. Accept names.
5. Choose "Download flat world"
6. Once the world has been imported to Bedrock Edition (v1.21.101), start a game with the imported world.
7. Find the spawn egg for "mycow".
8. Use the spawn egg.

Actual results

The log shows:

[Animation][error]-entity/test.entity.json | minecraft:client_entity | description | animation_controllers | child 'animation_controllers' not valid here.

[Json][error]-entity/mycow.entity.json | Material "mycow_cold" is referenced in file "entity/mycow.entity.json" but not defined.

[Geometry][error]-name_myco:mycow | name_myco:mycow | geometry not found?

The spawn egg shows the same icon as for a regular cow. However, the spawned mycow is invisible. Its shadow is visible, though.

Additional information

When starting from a creeper, there is also the same animation_controller error in the log. Additionally, the spawn egg icon is empty. If the lava damage for the creeper is changed to trigger from dirt instead, the invisible creeper explodes right after the invisible spawning, which (together with the cow's shadow showing up) indicates that the mob logic is being run and just the visual appearance is missing.

[mammerla]

I've fixed it so that the cow is updated to include the cold and warm variants. Though I made some improvements, still seeing some issues with creepers I'll look into.