This is done mainly so that downstream passes do not need to run
`CollectCFG` to store information that has already been computed but not
serialized.
This come at the cost of computing the CFG also of functions we don't
want to analyze in `DetectABI`.
The control-flow graph and all its hierarchy components
have been moved from `model` to `efa`. The CFG is now
serialized onto the LLVM IR module as a metadata.