NetherBridge -> NetherFortress

[bs2609]

Classes:

• MapGenNetherBridge -> MapGenNetherFortress
• StructureNetherBridgePieces -> StructureNetherFortressPieces

[Hornwitser]

If these classes are renamed, The field genNetherBridge of ChunkGeneratorHell should probably be renamed to genNetherFortress as well.

[kashike]

• net/minecraft/world/gen/structure/MapGenNetherBridge → net/minecraft/world/gen/feature/FortressStructure
• net/minecraft/world/gen/structure/StructureNetherBridgePieces → net/minecraft/world/gen/feature/FortressPieces