Thank you, that's just what I needed. However, I needed to change the names of some of the methods I was calling, as it seems they were obfuscated (I think that's the correct term).
Here is the code I used to access all dimension types:
for (DimensionType type : world.getServer().func_244267_aX().func_230520_a_()) {}
Here is the code I used to access all dimension Ids:
for (ResourceLocation location : world.getServer().func_244267_aX().func_230520_a_().keySet()) {}