This isn't enabled by default, relies upon
PolyhedralDev/Terra#264 to be fixed.

Terrain heightmaps should simply be multiplied
by the riverTerrainMask sampler to factor in
rivers.

Rework terrain to use a global heightmap

Remove autumnal_flats

Remove birch_flats

Remove taiga_flats

Remove evergreen_flats

Remove flowering_flats

Remove forest_flats

Remove xeric_plains

Remove jungle_flats

Remove chaparral_flats

Remove grass_savanna

Remove savanna

Remove tundra_hills

Remove dark_forest_hills

Remove rocky_wetlands

Remove autumntal_forest

Remove birch_forest

Remove taiga

Remove frozen_wetlands

Remove tundra_midlands

Remove rainforest

Remove evergreen_forest

Remove flowering_forest

Remove wetlands

Remove forest

Remove sandstone_wetlands

Remove jungle

Remove low_chapparal

Remove xeric_low_hills

Remove grass_savanna_low_hills

Remove savanna_low_hills

Remove rocky_sea_arches

Remove snowy_sea_arches

Remove snowy_terraced_mountains and snowy_terraced_mountains_river

Remove large_monsoon_mountains

Remove terracotta_sea_arches

Remove snowy_eroded_terraced_mountains

Remove desert_flats

Remove bamboo_jungle_flats

Remove _HILLS prefix from autumnal_forest biomes

Remove _HILLS prefix from birch forest

Remove _HILLS prefix from redwood forest

Remove HILLS_ prefix from taiga

Remove _HILLS prefix from rainforest

Remove _HILLS prefix from evergreen forest

Remove _HILLS prefix from flowering forest

Remove _HILLS prefix from forest

Remove _HILLS prefix from bamboo jungle

Remove _HILLS prefix from jungle

Remove _HILLS prefix from grass savanna

Remove _HILLS prefix from savanna

Done to make some biomes with matching palettes generate adjacent,
for example generate xeric biomes (more whiteish palette) adjacent
white desert, and arid spikes (more orangeish palette) adjacent
orange and red deserts.

I've decided these don't look very good in their current state
to generate so ubiquitously, they do however look pretty good
when used in overhangs so keeping them for that.

This is probably temporary but looks more in-place for now.

parabolicMap produces straight-ish lines across terrain
which doesn't look great, cubic interpolation should be
a better fit here.

This makes it so regular land biomes can generated adjacent
ocean, before this beaches tended to be far too common

This should mitigate some smaller microbiomes, and make
biome borders a bit more fuzzy.

Feature blending has resulted in mangrove trees generating
on less predictable blocks, so this ensures they will only
generate above water when on top of mud blocks. They will
still generate on any plantable block if underwater.

Mesas tend to get comically large at radius=300 (600 x 600 of perfectly flat space!) so reducing to 150

Add mob_rooms