IR Experimental: call-site profiling that feeds into inlining

* Added experimental call-site profiling in the IR interpreter
  and used it to drive inlining decisions.

  On bench_richards about ~7% speedup (~9% fewer instrs)
  On red_black_tree, about ~10% slowdown (~10% more instrs)

  To be investigated and experimented with more.
  Committing so others can partake of the fun as well.