instead, separate directories per GHC version at the expense of duplication.

* add dummy CHANGES and LICENSES to be compatible with cabal sdist
* split ghc-dependent code in plugin
* remove CPP from src-ghc92
* remove CPP from src-ghc94. split out src-ghc96
* remove CPP from src-ghc96
* apply fourmolu
* no CPP in ghc-specter-daemon
* format
* moduleNameString in GHCSpecter.Util.GHC. and then make Core2Core common
* use common GHCSpecter.Data.GHC.Core and minimize GHC version dep