feat(compiler): Optimize away unused recursive functions

[spotandjake]

This corrects our unused assignment optimization to cleanup unused recursive functions.

In order todo this I collect a context stack while iterating the anf_mapper and if the given id exists within the context path we don't mark it used.

let rec testRec = () => {
  let rec subTest = () => {
      testRec() // contexts: subTest -> testRec
  }
}

Closes: #1227