Access to file manipulation in data stage

[L0laapk3]

I would like to be able to use functions like `write_file` in the data stage.

My use case: I would like to store the actual image url of some icons/signals for later external use (labels on factoriomaps).
Currently, since its not possible to access those after the data stage (that I know of), my options are:
- output everything in a log file, which is not ideal as I'm launching multiple instances of factorio in parallel and would also like to support steam versions of the game which does not allow me access to the console output of factorio.
- dump everything in a big string somehow and read it back later and there use `write_file`.

[darkfrei]

+1, it's nice to make locale output or another lib generation for mod creating optimization.