Represents a mutable "snapshot" of an entity.
An instance of this class contains all the information needed to accurately reproduce the entity, provided that the instance was made correctly. In some implementations, it may not be possible to get a snapshot of entities correctly, so, for example, the NBT data for an entity may be missing.
This class identifies entities using its entity type string, although this is not very efficient as the types are currently not interned. This may be changed in the future.