Note [Use CBV semantics only for join points and workers]

A function with cbv-semantics requires arguments to be visible
and if no arguments are visible requires us to eta-expand it's
call site. That is for a binding with three cbv arguments like
`w[WorkerLikeId[!,!,!]]` we would need to eta expand undersaturated
occurrences like `map w xs` into `map (\x1 x2 x3 -> w x1 x2 x3) xs.

In experiments it turned out that the code size increase of doing so
can outweigh the performance benefits of doing so.
So we only do this for join points, workers and
specialized functions (from SpecConstr).
Join points are naturally always called saturated so
this problem can't occur for them.
For workers and specialized functions there are also always at least
some applied arguments as we won't inline the wrapper/apply their rule
if there are unapplied occurrences like `map f xs`.