Explore better register allocation

[pmenon]

During bytecode generation, we never reuse local variables (i.e., registers) in the frame (i.e., register file). This adds bloat to functions that have many temporaries.

This issue is to explore using a more intelligent register allocation algorithm. There's a trade-off as some algorithms are optimal but are complex. One option is linear scan. A simpler one might be from HyPer.