Use Prepack's evaluator for constant evaluation

If we switched out Babili's constant evaluation with the Prepack's I think this would push Babili to the winning side in terms of bundle size and potentially execution time. It doesn't have to use all of Prepack's fanciness -- just evaluating straightforward constants (no "abstract interpretation" and
"heap serialization").

On the downside, this will surely add to the compile time and might become more of a pressing problem (it can be then switched on/off via an option).

No files, tests, or entry points are named. Start by locating Babili's current constant-evaluation path and the relevant Prepack evaluator, then determine how straightforward constants could be handled without abstract interpretation or heap serialization. Define how compile-time cost and an optional on/off setting should be tested before attempting the integration.

Written by the indexing model from the issue text.