The blocks config option for spawning vanilla Minecraft structures does not generate objects in OTG 1.16

i.e. MinecraftObject(0,0,0,minecraft:igloo/igloo_bottom) in the .bo3 config

This hasn't worked for a long time I think (even for 1.12.2), will need to re-implement it. We can spawn these from registry (similar to Registry(), but they will still use their own spawn requirements/checks. Also I assume we'll have to spawn all normal bo blocks first, then the MinecraftObjects, to prevent them from being overridden.