Module hierarchy: GHC.Core (#13009)

Next step into introducing module hierarchy (cf #13009 (closed))

IMPORTANT: it requires some small changes in haddock. I have redirected the .gitmodules to my fork so don't merge as is.

 compiler/{coreSyn/CoreSyn.hs => GHC/Core.hs}
 compiler/{coreSyn/CoreArity.hs => GHC/Core/Arity.hs}
 compiler/{types => GHC/Core}/Class.hs
 compiler/{types => GHC/Core}/CoAxiom.hs
 compiler/{types => GHC/Core}/Coercion.hs
 compiler/{coreSyn/CoreFVs.hs => GHC/Core/FVs.hs}
 compiler/{types => GHC/Core}/FamInstEnv.hs
 compiler/{types => GHC/Core}/InstEnv.hs
 compiler/{types => GHC/Core}/Kind.hs
 compiler/{coreSyn/CoreLint.hs => GHC/Core/Lint.hs}
 compiler/{coreSyn/MkCore.hs => GHC/Core/Make.hs}
 compiler/{coreSyn/CoreMap.hs => GHC/Core/Map.hs}
 compiler/{simplCore => GHC/Core}/OccurAnal.hs
 compiler/{types => GHC/Core}/OptCoercion.hs
 compiler/{coreSyn/CorePrep.hs => GHC/Core/Prep.hs}
 compiler/{coreSyn/PprCore.hs => GHC/Core/Pretty.hs}
 compiler/{specialise => GHC/Core}/Rules.hs
 compiler/{coreSyn/CoreSeq.hs => GHC/Core/Seq.hs}
 compiler/{coreSyn/CoreOpt.hs => GHC/Core/SimpleOpt.hs}
 compiler/{coreSyn/CoreStats.hs => GHC/Core/Stats.hs}
 compiler/{coreSyn/CoreSubst.hs => GHC/Core/Subst.hs}
 compiler/{coreSyn/CoreTidy.hs => GHC/Core/Tidy.hs}
 compiler/{types => GHC/Core}/TyCoFVs.hs
 compiler/{types => GHC/Core}/TyCoPpr.hs
 compiler/{types => GHC/Core}/TyCoRep.hs
 compiler/{types => GHC/Core}/TyCoSubst.hs
 compiler/{types => GHC/Core}/TyCoTidy.hs
 compiler/{types => GHC/Core}/TyCon.hs
 compiler/{types => GHC/Core}/Type.hs
 compiler/{coreSyn/CoreUnfold.hs => GHC/Core/Unfold.hs}
 compiler/{types => GHC/Core}/Unify.hs
 compiler/{coreSyn/CoreUtils.hs => GHC/Core/Utils.hs}
 compiler/{simplCore => GHC/CoreToCore}/CSE.hs
 compiler/{simplCore => GHC/CoreToCore}/CallArity.hs
 compiler/{prelude/PrelRules.hs => GHC/CoreToCore/ConstantFold.hs}
 compiler/{stranal => GHC/CoreToCore}/DmdAnal.hs
 compiler/{simplCore => GHC/CoreToCore}/Exitify.hs
 compiler/{simplCore => GHC/CoreToCore}/FloatIn.hs
 compiler/{simplCore => GHC/CoreToCore}/FloatOut.hs
 compiler/{simplCore => GHC/CoreToCore}/LiberateCase.hs
 compiler/{simplCore/CoreMonad.hs => GHC/CoreToCore/Monad.hs}
 compiler/{simplCore => GHC/CoreToCore}/SetLevels.hs
 compiler/{simplCore/SimplCore.hs => GHC/CoreToCore/Simplifier.hs}
 compiler/{simplCore => GHC/CoreToCore}/Simplify.hs
 compiler/{simplCore/SimplEnv.hs => GHC/CoreToCore/Simplify/Env.hs}
 compiler/{simplCore/SimplMonad.hs => GHC/CoreToCore/Simplify/Monad.hs}
 compiler/{simplCore/SimplUtils.hs => GHC/CoreToCore/Simplify/Utils.hs}
 compiler/{specialise => GHC/CoreToCore}/SpecConstr.hs
 compiler/{specialise => GHC/CoreToCore}/Specialise.hs
 compiler/{simplCore/SAT.hs => GHC/CoreToCore/StaticArgs.hs}
 compiler/{stranal => GHC/CoreToCore}/WorkWrap.hs
 compiler/{stranal/WwLib.hs => GHC/CoreToCore/WorkWrapLib.hs}

Remaining source imports:

TODO: add Name and NameEnv underGHC.Core