machine: Fix passing of free variables to local functions

[marzipankaiser]

Now this uses all free Ids minus block labels, the name of this definition and constructor names,
and also adds the free Ids of called functions.

This also eta-expands functions passed directly as block parameters (since they are labels and thus, this will never work).

Additionally, adds a minor bugfix to transform(BlockType).

Resolves #217.

[marzipankaiser]

Marked as draft because this still does not work for:

def sumPaths(): Int = {
  val state = 0

  def explore(): Int = state
  def explore2(): Int = explore()

  explore2()
}

def main() =  println(sumPaths())

Notes:

• Here, state is not free in the lifted version of explore2. But it must still be passed on, so it can be forwarded to explore
• (Regarding the names: This code was gotten by successively shrinking the benchmark tree.effekt)

[marzipankaiser]

Since both the problem and the solution for #218 are closely related, I will fix that in this PR, too.

[marzipankaiser]

Fixes #218

[marzipankaiser]

@phischu This is what we talked about back then. Since it is now rebased and working, I will just merge it.