Support custom biomes in random teleport excluded biome list

[pop4959]

Fixes #5054.

Now possible via a provider. Unfortunately no better way of doing this, but at least this allows people to use custom biomes in their random teleport biome exclusions.

Would appreciate some further testing (I checked that the biome resolution works, and it shouldn't explode on old versions but I have not checked, not have I checked with a datapack).