savannah_ocean: use sandstone as filler

it grows from about Y320+ to Y31000+ (if possible)

use sandstone and stone on dunes, enlarge some filler depths

experimental: carefully re-add 1x candy 1x bacon biome

many biome tweaks & adjusted node usuage
update biome decorations to new biome configs
leave candy biome commented for now

add snowyfiller biome for biomegaps
add caves_ocean biome
adjust snowy decoration rules