Expose inner spawn data structures as public final. The reference shouldn't change so this should be acceptable. Makes mods function in a cleaner manner as well.
Method calls for Modifications interface order still matters.
Add Side effects handling to ModRemoveBiomeGroup:
Remove spawnlists associated with the biomegroup.
When updating biomegroup the new BiomeGroupId may not be identical to the old BiomeGroupId
Add Sideeffect handing for UpdateBiomeGroup Modification: if group has changed or is empty empty spawnlists and generate new ones
Add modification method to spawnlistregistry to add multiple spawnlistentries
Formatting to biomeGroupRegistry