Add call arity analysis to CakeML

[ordinarymath]

This issue is about implementing what Haskell calls arity analysis. https://www.joachim-breitner.de/publications/CallArity-ICFP2015-preprint.pdf.
I think this will involve a pass that just does eta expansion of functions before getting a more general inliner to inline the eta-expanded functions.
I suspect that the correctness proofs where Haskell ensure the condition of no extra work is being done for performance reasons will be a requirement in CakeML due to potentially effectful functions.