Traverse the charmap trie to reconstruct mappings instead of saving them

[Rangi42]

There's a fundamental issue with this approach that makes me not want to use it: it loses the order in which charmaps were defined, instead outputting them in the ASCII/UTF-8 byte order. (Even the mapped-value order would be more meaningful than that.)

Besides that, I still need to measure the performance benefit of not caching the mappings at definition time. I suspect that it was low; and the performance hit when actually making the dump file (admittedly a rare action) is visible.