Refactor implicit Prelude-Import
When a module does not explicitly import the Prelude, the frontend currently inserts an explicit import into the AST. This leads to a "wrong" output for the AST-Target.
Instead of adding the Prelude as an Import in the AST, it is sufficient to add it as an Import in FlatCurry (and AbstractCurry?), as well as directly enriching all environments with the entities from the Prelude .