Mitigate floating leaf blocks

[Astrashh]

Some trees use aggressive leaf fuzzing, resulting in floating leaf blocks:

This is fine if it is a rare occurrence but especially in more dense forests, it becomes a certainty that a leaf block will be floating in sight. Another possible solution is reworking the fuzzing based on a height map applied radially from the center of the leaf cluster, making floating blocks impossible.

[Astrashh]

Done in 99950c2c74e3659bc835bfe15e58372c89fe187c

These density changes should reduce the likelihood of floating blocks, however it will still be possible, albeit rarer.