Feature request name
NBT Support for entities (writing to)

Feature request description
Add support for spawning or creating entities with NBT.

Feature request reason
Currently, we can read NBT from an entity via getNBT(), but we cannot set that NBT nor can we spawn an entity with custom NBT (IData). Mainly used for spawning Better With Addons spirits, but it would have numerous other uses as well.

Feature request dependencies
N/A

It appears that there is an update(IData) function - however, it does nothing because it calls a method without using the method's return value at line 66 of https://github.com/CraftTweaker/CraftTweaker/blob/1.12/CraftTweaker2-MC1120-Main/src/main/java/crafttweaker/mc1120/data/NBTConverter.java
Or is the IData value that's passed a reference?

idata is passed as a reference