Ancient Cities should extend the Deep Dark

Ancient Cities and the Deep Dark go hand in hand, so it always comes off as a little weird when I find an Ancient City that isn't covered in Sculk. Sometimes Ancient Cities will be very clean and Sculk-free, or sometimes a structure in the Ancient City will be covered in Sculk, but it isn't actually in the Deep Dark Biome, so it feels out of place. The Sculk is part of what the Ancient City is, so it feels weird to find parts of the Ancient City without and Sculk. 

I think the Ancient City should extend the Deep Dark biome, here's how: upon world generation, the Ancient City will check to see if the whole structure and all its components are fully within the Deep Dark Biome. If not, the biome will be extended to include the full structure, so that the entirety of the Ancient City is within the Deep Dark and covered in Sculk. This may mean pushing back on Dripstone Caves or Lush Caves and making them slightly smaller