Previously, caverns confused tunnel generation causing biome top and filler
nodes to appear in caverns.
Split 'generateCaves()' into 2 functions to separate tunnel and large
randomwalk cave generation.
In each mapgen re-order cave generation to generate tunnels before caverns.
Add new biome fields 'node_dungeon', 'node_dungeon_alt', 'node_dungeon_stair'.
If 'node_dungeon' is not defined dungeons fall back to classic behaviour.
Remove messy and imprecise dungeon material code from 'generateBiomes()'.
Code deciding dungeon materials is now in 'generateDungeons()' and uses the
biome at mapchunk centre for more precision.
Remove hardcoded 'MG_STONE' types as long intended.
* Fix many issues reported by clang-tidy
We have many issues in code related to some performance to float <-> double.
Clang-tidy reported it in performance-type-promotion-in-math-fn
I fixed many of them. It's not ready for a promote to blocking
Also fix some value which should be const-ref
