Have tools follow mapped .json on original .TBC

[Gamnn]

I had a thought it would save time and space for ld-discmap to only output a mapped .json, and have the tools use the original TBC with it.

It could still export a mapped .TBC as an option, however.

[atsampson]

I like the "output a mapped .json" idea, where each field indicates which field in which input file it should be, but I think I'd rather have a separate tool that reads the mapped .json and outputs a corrected .tbc which you could pipe into the existing toolchain (or write to a file). If all the tools have to understand reading "mapped .json", then they would also have to produce an unmapped .json file as part of their output to feed to the next tool in the chain, which is a pain with piped output.