light calculations repeatedly looks up the same chunk while going
down on the Y access. Pass the chunk to it to skip many round trips
to the map lookup process.
while the gains arent as big since we have last access cache, it
should hopefully avoid many callstacks of depth and improve inlining,
as well as avoids entering a synchronized code block.
The avoiding of entering synchronized section is the main goal here.
The server triggers light recalculations even if the new block
is the same as the old block. At this time, BlockData Properties
do not impact light calculations.
So the only way light should change, is if the block itself
changes from 1 block to another.
Additionally, as of 1.13, water now only blocks 1 light level
instead of 3, meaning that light level decreasing is the same as air.
This means, transitions between water and air also do not need
to recalculate light, which saves a TON of updates caused by
fluids flowing.
Aikar