This introduces a new id data block with type ID_SIM.
The RNA part of this change is disabled by default for now.
The corresponding cmake option is WITH_SIMULATION_DATA_BLOCK_RNA.
The new data block does not yet have an embedded node tree.
I want to add that separately.
This is part of T73324.
The set of files I changed is based on rBb0a1cf2c9ae696.
However, I had to change fewer files, because I did not add a new object type.