Add biome return value for shipwrecks in isViableStructurePos, similar to villages

[AeroAstroid]

Convenient to have for analysis, as beach vs. ocean have different behavior when rolling for ship type and orientation (and thereby, the resulting loot)

[AeroAstroid]

Didn't realize this before but this causes a collision because regular oceans are ID 0 which clashes with the return value for an invalid structure position, my apologies. Still, I think there's value in refactoring this function to maybe add a pointer to hold a biome return value, in a similar way to how getStructurePos does so for position. I'll keep this as a draft for the time being if that's fine