Implement cross-chunk-border lighting propagation

[dktapps]

Problem description

Crops in shadowed areas in e.g. overhangs will currently not grow correctly due to the lack of cross-chunk-border light propagation.

Basically: If the only available light source for crops is in an adjacent chunk, currently the crops won't know about the light from that light source, because we don't propagate it across chunk borders.

This would also lead to problems with mob spawning.

Proposed solution

Implement pass 2 light propagation as described here: https://github.com/dktapps/lighting-algorithm-spec?tab=readme-ov-file#pass-2-propagate-light-across-chunk-borders

We already have pass 1 light propagation (Chunk->isLightPopulated() === true means "has pass1 lighting").

Why hasn't this been done already?

It's not hugely difficult, but it is a bit complicated to implement and doesn't provide a huge amount of benefit at present. It could also cause a hit to performance if done poorly.

• Chunk would need to add a set of flags to track which pass2 positions it's received light propagation from
• Adjacent chunks would need to update their pass2 flags when an adjacent chunk is replaced

Alternative solutions that don't require API changes