Revise river-port placements

[Goosius1]

• Currently placing a river port checks for the biome, but it decides how to check based on the "check by block" config, which is quite messy.
• In addition, it always looks in the middle of the chunk, which is not super clever, because the river might not be there
• To fix these issues:
  • First, maybe check all the surface blocks for a river... Or check where the player is standing. We'd have to do the same thing for ocean port placements.
  • As for the biome, perhaps just remove that config entirely, and always try to use the block biome. If that doesn't work in the wild, we may have to re-add the config back for placement scanning. I saw that valoria were getting incorrect biome info at one point but......I suspect that is actually because they had not switched the config to the right settings. I think getting it by block might work all round
  • As for the land validation job, let that always use the material check anyway, as its entirely reliable.