This came from slicedlime's download links. Last I knew, the guy works for Mojang. So yes, I assume it's somewhere in the vanilla jar, but probably obfuscated. I say this because you can pull any jar for a version of Minecraft you've played right from the game's folders, but when you look into the data folder of the jar, the worldgen folder isn't there until you hit 1.19.3. This is probably why he stopped posting them at that point.
So to find the jar on a PC it's AppData/Roaming/.minecraft/versions/ and in there will be folders for every version you've ever played. In each of those folders is a matching jar. This means that you'll probably be able to find it all in the external libraries of your workspace as well.