Support for Java Edition 1.19.3

[nahkd123]

Java Edition 1.19.3 has just been released. There are some changes to packs:

• Resource pack version is now 12.
• Introduction of feature flags.
• Backward compatibility for resource packs with version 3 and 4 has been removed.
• Some textures loading changes.
  • Introduction of atlases/. Mainly for improving textures loading performance.

There are more technical changes, which can be found here.

There are some tasks that need to be done to support 1.19.3:

• Feature flags on index files (multipacks.index.json).
• Atlas files generation.
• Perhaps we should remove pre-flattening pack versions? (version 3 and 4)